CiteULike: Tag pine

Plant regeneration from callus cultures derived from mature zygotic embryos in white pine (Pinus strobus L.).

W Tang — 2006-07-20T14:35:01-00:00

Plant Cell Rep, Vol. 24, No. 1. (April 2005), pp. 1-9.

Plant regeneration via adventitious shoot organogenesis from callus cultures initiated from mature embryos in white pine (Pinus strobus L.) was achieved in this study. Callus cultures were induced from mature embryos cultured on PS medium supplemented with 2,4-dichlorophenoxyacetic acid, alpha-naphthaleneacetic acid, or indole-3-acetic acid. Adventitious shoot regeneration from callus cultures was induced on medium containing 2 microM indole-3-butyric acid (IBA) and 3-12 microM N(6)-benzylaminopurine, thidiazuron (TDZ), or 6-(gamma,gamma-dimethylallylamino) purine. Sucrose was the most suitable sugar for adventitious shoot organogenesis in white pine. Shoot organogenesis was improved by treatment at 4 degrees C for 6 weeks. The frequency of adventitious shoot formation increased when 0.1 mM putrescine was added to basal medium supplemented with 6 microM TDZ and 2 microM IBA. Putrescine improved adventitious shoot organogenesis by decreasing lipid peroxidation. These findings provide useful information on adventitious shoot organogenesis and may be valuable to genetic transformation in white pine.

Influence of the embryonal-suspensor mass (ESM) sampling on development and proliferation of maritime pine somatic embryos.

A Ramarosandratana — 2006-07-20T14:28:33-00:00

Plant Sci, Vol. 160, No. 3. (5 February 2001), pp. 473-479.

Two maturation media with high and low concentration of gellan gum were used to evaluate the maturation performances of four maritime pine ESM (embryonal-suspensor mass) lines. The maturation performance is influenced by sampling modalities; the outer part of the ESM yielded more cotyledonary embryos than the inner part or the whole colony. ESM lines showing several stage 1 embryos at the periphery (spiky) were more productive than those for which stage 1 embryos were rarely visible (smooth). This latter group develop preferably stage 3 embryos on the maturation medium containing high concentration of gellan gum. Biomass production is higher on a medium containing low concentration of gellan gum. However, sampling modalities did not affect the biomass production, and no relation was found between the biomass production and the maturation performance of each line. Stage 3 embryos developed on the medium with low concentration of gellan gum (0.45%, w/v) were shorter than those developed on medium with 0.9% of gellan gum. These short embryos were not able to germinate whereas about 48% of germination was reached with the longest embryos. The ability to develop primary root is dependent on the genotype while epicotyl elongation was observed among all lines.

The role of sucrose during maturation of black spruce (Picea mariana) and white spruce (Picea glauca) somatic embryos.

Driss Iraqi — 2006-07-20T14:27:40-00:00

Physiol Plant, Vol. 111, No. 3. (March 2001), pp. 381-388.

The present study was conducted to understand the role of sucrose in the medium on the maturation of black spruce and white spruce somatic embryos. A maturation medium containing 6% sucrose, which hydrolyzed into glucose and fructose, gave significantly more embryos than a medium containing 3.16% of each glucose and fructose. Preventing the complete sucrose hydrolysis by a daily transfer of the tissues onto fresh medium significantly decreased the yield of somatic embryos compared to when sucrose was allowed to complete its hydrolysis. This reduction was not due to the manipulation of the tissues during the transfer, since a daily in situ transfer did not affect embryo production. To verify if the better embryo production observed on a medium containing 6% sucrose was due to the increasing osmotic pressure of the medium, this increasing osmotic pressure was simulated with a sequence of media containing different concentrations of glucose and fructose. Unexpectedly and for both species, this simulation did not improve somatic embryo production, which stayed similar to the one obtained on constant osmotic pressure. To understand these results, embryos produced on the different treatments were analyzed in terms of sucrose, glucose, fructose and starch levels and protein contents. The embryo carbohydrate content was independent from the carbohydrate used in the maturation medium. However, embryos matured on 6% sucrose allowed to hydrolyze during the maturation period contained significantly more soluble and insoluble proteins than embryos matured on any other treatment. Furthermore, embryos with a higher protein content also exhibited a higher epicotyl appearance frequency. The role of sucrose as a regulatory factor during the maturation of spruce somatic embryos is discussed.

Early selection improves clonal performance and reduces intraclonal variation of Norway spruce plants propagated by somatic embryogenesis.

KA Högberg — 2006-07-20T14:26:39-00:00

Tree Physiol, Vol. 23, No. 3. (February 2003), pp. 211-216.

Height growth during the first and second growth periods (i.e., the June-September period in consecutive years) and intraclonal variation were assessed in 13 Norway spruce (Picea abies (L.) Karst.) clones propagated by somatic embryogenesis. The plants were acclimatized and grown in a greenhouse until mid-July and then transferred outdoors. The clonal mean heights after the first and second growth periods were lower for somatic embryo plants than for seedlings from corresponding families sown at the time of somatic embryo plant ex vitro transfer, because a large proportion of somatic embryo plants were small. We determined whether certain selection criteria at ex vitro transfer can be used to identify somatic embryo plants with height growth characteristics comparable with those of seedlings. Epicotyl length and presence of lateral roots proved to be important parameters for selection, whereas main root length was less useful. A combined selection for somatic embryo plants with lateral roots and with an epicotyl length exceeding 8 mm resulted in taller plants and reduced intraclonal variation after the first and second growth periods. The growth of somatic embryo plants selected in this way was similar to that of seedlings from the corresponding families. We conclude that selection according to these criteria at ex vitro transfer can result in improved performance of clonal stock propagated by somatic embryogenesis.

Accounting for population variation improves estimates of the impact of climate change on species’ growth and distribution

Gregory O’neill — 2008-05-15T12:13:29-00:00

Journal of Applied Ecology, Vol. 0, No. 0. (0), pp. ???-???.

Summary 1. Large differences exist in the predictions of plant responses to climate change among models that consider population variation and those that do not. Models that treat species as homogeneous entities typically predict net positive impacts of climate change on temperate forest productivity, while most studies that consider adaptive genetic variation within species conclude that the impacts of climate change on forest productivity will be negative. 2. We present a modelling approach that predicts plant responses to climate change using both ecological and genetic variables. The model uses growth data from multi-site provenance trials together with climate data for provenance source locations and test sites to predict distribution and productivity of tree populations under climate change. We used an extensive lodgepole pine Pinus contorta provenance data set to illustrate the model. 3. Spatially explicit predictions of the impacts of climate change on production were developed and suggested that different populations of lodgepole pine will respond very differently to climate change. Large production losses will be seen in many areas, although modest production increases may occur in some areas by 2085. The model further projects a significant redistribution of the species’ potential habitat northwards and upwards in altitude over the next several decades. 4. Synthesis and applications. This study points to the need to consider population differences when modelling biotic responses to climate change, and suggests that climate change will render populations maladapted in many areas. The model also provides a key tool potentially to mitigate climate change impacts by identifying populations expected to be best adapted throughout the next generation of forests. Finally, the study highlights the value of wide-ranging long-term provenance tests in addressing key issues in ecology and climate change.

Hydraulic design of pine needles: one-dimensional optimization for single-vein leaves

Maciej Zwieniecki — 2006-04-07T20:25:38-00:00

Plant, Cell & Environment, Vol. 29, No. 5. (May 2006), pp. 803-809.

MicroRNAs in loblolly pine (Pinus taeda L.) and their association with fusiform rust gall development

Lu — 2007-09-07T10:57:11-00:00

The Plant Journal, Vol. 51, No. 6. (September 2007), pp. 1077-1098.

Glacial vicariance in Eurasia: mitochondrial DNA evidence from Scots pine for a complex heritage involving genetically distinct refugia at mid-northern latitudes and in Asia Minor

Krassimir Naydenov — 2007-11-23T14:30:10-00:00

BMC Evolutionary Biology, Vol. 7 (22 November 2007), 233.

Restoration of natural broad-leaved woodland in Central Europe on sites with coniferous forest plantations

Stefan Zerbe — 2006-03-28T10:02:54-00:00

Forest Ecology and Management, Vol. 167, No. 1-3. (15 August 2002), pp. 27-42.

The creation and restoration of natural woodland serving diverse socio-economic as well as nature conservation purposes has become a major objective of sustainable forestry throughout Europe. There is a main focus on the conversion of anthropogenous coniferous forests, which are widely spread in the Central European lowlands and mountain ranges, into natural broad-leaved forests. For ecological as well as economic reasons, the integration of natural regeneration processes into conversion management is considered an important task. Taking the woodland of the Menzer Heide (NE Germany), a typical Pleistocene landscape in the northern Central European lowlands as an example, a vegetation analysis of the Scots pine (Pinus sylvestris L.) plantations dominating in this area is presented. As the main results, (1) two communities are differentiated within the present-day pine plantations on the oligotrophic and acidic sandy soils. Indicated by different species compositions, the Dicranum-community and the Oxalis-community occur, the latter growing on sites with higher nutrient availability. (2) The comparison of an historical with the present vegetation analysis reveals an increase of nutrient availability in recent decades, most probably strongly related to the natural soil regeneration of the formerly exploited forest sites. (3) From the results of the vegetation analysis, including records of species and individual numbers of naturally rejuvenated trees, future stand development scenarios can be derived. Thus, the Oxalis-community may directly develop into oak-beech and beech stands as natural forests. In the long term, the Dicranum-community will pass a regeneration stage with pine and oak, probably further developing towards natural oak-beech and beech forests. In conclusion, decisions regarding extensive or intensive management, aiming at the conversion of coniferous plantations into natural broad-leaved forests, can be made following observation of the natural regeneration processes in the present-day stands. By utilising the natural regeneration processes and by applying only a few controlling silvicultural measures, a low-energy and cost-effective conversion of the forests can be accomplished.

Using mechanistic modeling within forest ecosystem restoration

Stephan Pietsch — 2006-03-28T09:45:35-00:00

Forest Ecology and Management, Vol. 159, No. 1-2. (1 April 2002), pp. 111-131.

In Europe, fast growing tree species such as Norway spruce and Scots pine were promoted in large areas typically covered with broadleaf or mixed species stands to increase commercial timber growth. Recent research suggests that such secondary coniferous stands may have an increased susceptibility to environmental stress factors because of soil nutrient depletion as well as retarded litter decomposition. One option to increase the resilience of such stands is to reintroduce broadleaf trees because one species may directly benefit from the presence of another. A method to assess such effects and how their impact may change over time is the adaptation of mechanistic models. Such models integrate the main biogeochemical and physiological processes and are specifically designed to describe the interaction between plants and the environment. The purpose of this study is to enhance the ecophysiological representation of single tree species within an existing mechanistic model, a pre-condition for assessing forest ecosystem restoration scenarios. We changed ecophysiological constants using published literature related to Norway spruce and common beech for a wide range of central European forests and evaluated model predictions using observations on stand transpiration, seasonal water balance, leaf area index, photoassimilation, tree volume, tree ring size, and soil and litter carbon and nitrogen content. A model validation, using an independent data set on tree volume, soil carbon and nitrogen content from a total 44 spruce and beech stands across the northern part of the Austrian Alps, exhibited no bias between model predictions and field observations.

Fire, fuels and restoration of ponderosa pine Douglas fir forests in the Rocky Mountains, USA

William Baker — 2007-01-20T17:44:08-00:00

Journal of Biogeography, Vol. 34, No. 2. (February 2007), pp. 251-269.

Comparing the Importance of Seedbed and Canopy Type in the Restoration of Upland Thuja occidentalis Forests of Northeastern Minnesota

Meredith Cornett — 2006-10-19T19:42:38-00:00

Restoration Ecology, Vol. 9, No. 4. (2001), pp. 386-396.

Abstract In cold-temperate ecosystems of the upper Great Lakes Region, evergreen conifer-dominated forests were once common. As a result of past management practices, early-successional deciduous forests now dominate the landscape. Embedded in this matrix are stands of shade-tolerant conifers, including Thuja occidentalis. For the past several decades, large-scale T. occidentalis regeneration in remnant T. occidentalis and adjacent Betula papyrifera forests has not occurred. Using a combination of restoration experiments and field surveys at three study sites on the Lake Superior Highlands, Minnesota, U.S.A., we examined safe sites for T. occidentalis regeneration under both Thuja and Betula canopy types. This study focused on the colonization and establishment phases of regeneration, differentiating among safe-site components for T. occidentalis. Seedbed type determined colonization success, with higher rates on conifer logs than on B. papyrifera logs, mounds, or pits. Mortality rates for seedlings on natural decayed wood seedbeds were higher under Thuja canopy than under Betula canopy, but the reverse was true for seedlings on manipulated seedbeds, suggesting that seedbed type was more important than the dominant canopy type. Growth rates for seedlings on moved log segments were greater under the Betula than the Thuja canopy type, but seedlings on natural decayed wood seedbeds did not exhibit this difference. Results indicated that T. occidentalis regeneration was more limited in Betula forest by seedbed availability, while in Thuja forest canopy conditions were more limiting.

Does Weeding Promote Regeneration of an Indigenous Tree Community in Felled Pine Plantations in Uganda?

Colin Chapman — 2006-10-19T19:37:22-00:00

Restoration Ecology, Vol. 10, No. 2. (2002), pp. 408-415.

Abstract The use of plantations to manage extensive tracks of deforested lands in the tropics is a conservation strategy that has recently received considerable attention. Plantation trees can promote seed dispersal by attracting dispersers and creating favorable site conditions, leading to increased germination and establishment of indigenous trees. Subsequently, plantation trees can be harvested for profit or left to senesce, leaving a native tree community. We evaluated the effect of vine, grass, and shrub cutting (weeding) over a 3-year period on regeneration of indigenous trees subsequent to the removal of plantation softwoods in Kibale National Park, Uganda. Counter to what would be expected if weeding released trees from competition, we found no difference in the total number of stems or in the stems greater than 10 cm diameter at breast height between control and weeded plots; there were more stems greater than 1 cm diameter at breast height in the control plots. For species found in both control and weeded plots, the maximum size of individuals did not differ. At the end of the study, 61 species were found in the control plots and 43 species were found in the weeded plots, and in both types of plots the three most abundant species were the same. The number of species and stems classified as early or middle successional species did not differ between weeded and control plots. The fact that weeding did not promote regeneration of indigenous trees after the removal of plantation trees illustrates the importance of evaluating and field-testing potential management options.

Using stand replacement fires to restore southern Appalachian pine-hardwood ecosystems: effects on mass, carbon, and nutrient pools

James Vose — 2006-05-16T15:26:25-00:00

Forest Ecology and Management, Vol. 114, No. 2-3. (22 February 1999), pp. 215-226.

Pine-hardwood ecosystems in the southern Appalachians are in serious decline due to fire exclusion and insect infestations. Fire has been advanced as a tool to restore these ecosystems, yet there are few studies evaluating overall ecosystem effects. Our objectives were to evaluate the effects of stand restoration burning on forest floor nitrogen (N) and carbon (C) pools, and soil and stream chemistry. We measured changes in forest floor (coarse woody debris, small wood, litter, and humus) mass, N, and C; changes in soil chemistry (calcium (Ca), potassium (K), magnesium (Mg), cation exchange capacity (CEC), pH, C, and N); and changes in stream nitrate (NO3). Results showed that significant reductions in mass, N, and C occurred only for litter and small wood on the ridge, where N losses were 52.9 kg ha-1 for litter and small wood combined. No significant effects were observed on the mid- or lower slope of the treatment watershed. Losses on the ridge are considerably lower than losses which occur with alternative burning treatments used in the region, such as the fell and burn treatment. Soil and stream chemistry showed no response to burning. Spatial heterogeneity in fire intensity (combustion temperatures ranged from 800[deg]C) and severity associated with stand replacement burning results in a mosaic of fire effects and considerably less consumption and subsequent nutrient losses.

The acceleration of succession for the restoration of the mixed-broadleaved Korean pine forests in Northeast China

Xiongwen Chen — 2006-05-16T14:37:03-00:00

Forest Ecology and Management, Vol. 177, No. 1-3. (7 April 2003), pp. 503-514.

There are large amounts of clear-cuts and secondary forests in Northeast China. In order to preserve habitats of biodiversity and decrease ecological disasters, it now becomes urgent to restore them to the climax. An adapted forest dynamics model is used to simulate the change in tree species composition, density, and stem productivity of forests regenerating from clear-cuts of the mixed-broadleaved Korean pine forest (MKPF) and the introduction of species over 100 years in the region. The model shows that the restoration of climax forests on these sites can be accelerated by the introduction of proper tree species. For the current secondary forest of Quercus mongolica, Populus davidiana and Betula platyphylla, if the medium-type of shade tolerant tree species are introduced into the communities, the dynamics of tree species will change, and the stem productivity will decrease by 20%. If Larix olgensis is introduced into the forest communities, it will become dominant in the forests, with stem productivity increasing about 110%. If Pinus koraiensis is introduced, it will dominate the communities after 90-100 years, although the density and stem productivity will not change significantly. If P. koraiensis is introduced into the current secondary forest of medium-type trees, the dynamics of the forest will change significantly and the growth of medium-type trees will increase after 20 years. If the medium-type trees are introduced into the plantations of pure P. koraiensis, both the tree density and stem productivity will increase dramatically, and the earlier stem divergence, earlier branching, of P. koraiensis can be improved.

Evaluating ponderosa pine regeneration rates following ecological restoration treatments in northern Arizona, USA

J Bailey — 2006-05-16T14:09:05-00:00

Forest Ecology and Management

Abstract Ecosystem restoration is emerging as a dominant ponderosa pine (Pinus ponderosa var. scopulorum) forest management objective in the semi-arid southwestern USA. Restoration consists predominantly of mechanical thinning in overly dense stands and reintroduction of ground fire, and therefore can meet a variety of community and agency objectives associated with forest ecosystem health, wood production, fire protection, recreation and scenic beauty. Ecosystem restoration and long-term multi-aged stand management creates the growing space, microclimate and seedbed conditions necessary for natural regeneration via density reduction and regular understory burning. Several long-term research studies have demonstrated regeneration >100 seedlings/ha within a few years of overstory treatment when a relatively dense overstory canopy is left as a seed source; based on the literature, the reduced density of overstory seed-producing trees following restoration treatment still supplies sufficient viable seed over time for regeneration. Our remeasurement data of treated sites showed only 18–41 seedlings/ha in the absence of fire due perhaps to the reduced density of seed-producing overstory trees or lack of adequate (fire prepared) seedbed. Repeated prescribed burning of surface fuels can enhance the seedbed, but limits seedling survival typically during the first two decades. Survivors develop into fire resistant saplings at 10 cm stump diameter and 3 m height. Seedling density in a restoration study plots that has received two burning treatments, in 1992 and 1998, was only 12 seedlings/ha. Seedling density in the 30 growing stock level treatments at Taylor Woods averaged only 7 seedlings/ha following one burning cycle. However, even this relatively low natural regeneration rate is sufficient to supply the 3.6 trees/ha/ decade needed to sustain tree densities like those present before Euro-American settlement. # 2002 Elsevier Science B.V. All rights reserved.

Comparing ecological restoration alternatives: Grand Canyon, Arizona

PZ Fule — 2006-05-16T13:52:01-00:00

Forest Ecology and Management, Vol. 170, No. 1. (2002), pp. 19-41.

Three treatments designed to initiate the process of restoring the surface fire regime and open forest structure of a southwestern ponderosa pine forest were compared on the Kaibab National Forest along the Grand Canyon’s South Rim. The treatments were: (1) full restoration (FULL)—thinning trees to emulate stand structure prior to fire regime disruption ca. 1887, forest floor fuel treatment, and prescribed burning, (2) minimal thinning (MIN)—removing young trees only around living old-growth (pre-1887) trees, fuel treatment, and prescribed burning, (3) burn-only (BURN)—representing the current management policy in Grand Canyon National Park (GCNP), and (4) CONTROL. Each treatment was applied to a 12 ha unit. Compared to reconstructed 1887 conditions, all study sites were much more dense prior to treatment (94–176 trees/ha in 1887, compared to 783–3693 trees/ha in 1997). However, basal area increases were less striking (12.6–20.3 in 1887, 17.5–27.0 m2/ha in 1997), reflecting past harvest and dwarf mistletoe reduction treatments that removed many large pines. In 2000, 1 year after treatment, tree densities were reduced to 11, 23, and 37 of pre-treatment levels in the FULL, MIN, and BURN treatments, respectively. Understory plant communities showed significant declines in richness and plant frequency across years, probably due to a severe drought in 2000 (60% of average precipitation). No differences in plant communities were observed across treatments, despite the mechanized disturbance associated with tree removal in the FULL treatment. Prescribed fire behavior (flame length, flaming zone depth) and effects (bole char, crown scorch) were similar across all three burned treatments. Simulated fire behavior under dry, windy conditions was reduced in all three treatments compared to the control. The FULL treatment was much less susceptible to crownfire due to reduced crown bulk density and crown fuel load and increased crown base height. Crownfire susceptibility of the BURN treatment was only slightly reduced, while the MIN treatment was intermediate. Compared to the reference conditions of forest structure, the FULL treatment represented the most rapid and comprehensive restoration treatment, although the residual stand was at the low end of historical density. The BURN treatment thinned many small trees but had minor effects on crownfire susceptibility. Effects of the MIN treatment fell between FULL and BURN. The experimental treatments may be useful for the creation of defensible firebreaks near developments, roads, and boundaries with the FULL treatment, supplemented by MIN and BURN treatments over larger areas.

Native forest regeneration in pine and eucalypt plantations in Northern Province, South Africa

Coert Geldenhuys — 2006-04-21T09:30:03-00:00

Forest Ecology and Management, Vol. 99, No. 1-2. (December 1997), pp. 101-115.

Commercial plantations in South Africa have been established mainly in grasslands adjacent to native forest which occur as small, scattered patches, restricted to valleys and scarps by regular fires in the adjacent fire-prone grasslands. Understorey vegetation was sampled in plantation stands of different age of Pinus patula, and old stands of P. elliottii, P. taeda and Eucalyptus saligna, growing on the forest margin. The study was done in two areas in Northern Province, South Africa (23[deg]S to 25[deg]S, and 30[deg]E to 31[deg]E): Woodbush-De Hoek along the Eastern Escarpment, and Entabeni on Soutpansberg mountains. The area receives 1200 to 1900 mm rain per annum, mainly during summer. Two hypotheses were tested: understorey colonisation by native plant species is strongly influenced by the overhead plantation species; and abundance and diversity of indigenous woody and herbaceous species increase with increasing stand age. A total of 170 species were recorded on 62 plots of 78.5 m2 each, and included all major growth forms present in the surrounding forest, except epiphytes. Trees were represented by 62 species, but only 18% of these occurred in more than 10% of the plots. Seventy-two percent of the 95 tree, shrub and climber species are animal-dispersed but only 22% of the animal-dispersed species occur in more than 10% of the plots. Mean clean bole length of the plantation stand gave the best regression coefficients with species richness, stem density, mean DBH and mean height of the woody regeneration, all of which increased with stand age. There was no clear pattern in understorey species composition among the different plantation species. Site factors such as substrate (geology) and temperature (altitude and radiation index) had a strong correlation with species composition and density of understorey vegetation. The results do demonstrate a useful successional process which could be used to achieve specific management objectives at relatively low costs. Potential applications of this succession process are manipulation of tree stands (commercial plantations or invader plants) to restore native forest biodiversity, control of understorey weeds in commercial plantations, and growing of useful crops under tree canopies.

Short-Lived Tree Species and Their Role as Indicators for Plant Diversity in the Restoration of Natural Forests

Daria Kreyer — 2006-02-07T09:38:09-00:00

Restoration Ecology, Vol. 14, No. 1. (March 2006), pp. 137-147.

Dense Packing and Symmetry in Small Clusters of Microspheres

Vinothan Manoharan — 2007-04-04T07:42:56-00:00

Science, Vol. 301, No. 5632. (25 July 2003), pp. 483-487.

When small numbers of colloidal microspheres are attached to the surfaces of liquid emulsion droplets, removing fluid from the droplets leads to packings of spheres that minimize the second moment of the mass distribution. The structures of the packings range from sphere doublets, triangles, and tetrahedra to exotic polyhedra not found in infinite lattice packings, molecules, or minimum-potential energy clusters. The emulsion system presents a route to produce newcolloidal structures and a means to study howdifferent physical constraints affect symmetry in small parcels of matter. 10.1126/science.1086189

Preparation of monodisperse PMMA microspheres in nonpolar solvents by dispersion polymerization with a macromonomeric stabilizer

Sascham Klein — 2007-05-27T21:14:34-00:00

Colloid & Polymer Science, Vol. 282, No. 1. (1 December 2003), pp. 7-13.

We discuss a dispersion polymerization procedure for preparing monodisperse and micron-sized poly(methyl methacrylate) (PMMA) particles in hexanes with methacryloxypropyl-terminated polydimethylsiloxane stabilizers. We investigate the effects of the stabilizer molecular weight, stabilizer concentration, and monomer concentration on the particle size and polydispersity. We find that a minimum molecular weight of 10 000 g/mol is necessary to synthesize colloidally stable PMMA dispersions. The particle polydispersity is minimal (=5%) for stabilizer to monomer weight ratios of 0.02 to 0.1, while PMMA particles prepared under conditions outside this range are polydisperse. The particle diameter can be varied from 0.4 to 1.5 µm by appropriate choices of stabilizer and monomer concentrations. Stable PMMA suspensions can be prepared at up to 26.3% solids. The dispersions are stable in most liquid aliphatics, and are monodisperse enough to form ordered domains at high concentration. This single-stage synthesis, requiring only commercially available materials, may be of interest to those seeking a simple way to prepare highly monodisperse non-aqueous dispersions in the micron size range.

Yielding and Rearrangements in Disordered Emulsions

P Hébraud — 2008-04-25T19:52:15-00:00

Physical Review Letters, Vol. 78, No. 24. (16 June 1997), 4657.

Multiple Light-Scattering Probes of Foam Structure and Dynamics

DJ Durian — 2007-04-18T19:27:19-00:00

Science, Vol. 252, No. 5006. (3 May 1991), pp. 686-688.

The structure and dynamics of three-dimensional foams are probed quantitatively by exploiting the strong multiple scattering of light that gives foams their familiar white color. Approximating the propagation of light as a diffusion process, transmission measurements provide a direct probe of the average bubble size. A model for dynamic light scattering is developed that can be used to interpret temporal fluctuations in the intensity of multiply scattered light. The results identify previously unrecognized internal dynamics of the foam bubbles. These light-scattering techniques are direct, noninvasive probes of bulk foams and therefore should find wide use in the study of their properties. 10.1126/science.252.5006.686