Drying dissipative structures of thermosensitive gel spheres of poly (N-isopropylacrylamide). Influence of gel size

Drying dissipative patterns of de-ionized suspensions (colloidal crystal-state at high concentrations) of the thermosensitive gels of poly (N-isopropylacrylamide) with various sizes (ca. 400–1,500?nm in diameter at 20?°C) were observed at 20 and 45?°C on a cover glass, a watch glass, and a Petri glass dish. The broad rings were observed and their size decreased as gel concentration decreased. Formation of the monodispersed agglomerated particles and their ordered arrays were observed irrespective of gel size. The macroscopic flickering spoke-like patterns were observed for the gel spheres from 70 to 600?nm in diameter at 20?°C, but almost disappeared for extremely large spheres, poly(N-isopropylacrylamide)(1500-5). This work clarified the formation of the drying microscopic structures of (a) ordered rings, (b) flickering ordered spoke lines, (c) net structure, and (d) lattice-like ordered structures of the agglomerated particles. The ordered rings became rather vague as gel size increased. The large net structures formed so often for large gels. Size effect on the lattice patterns was not recognized so clearly. The role of the electrical double layers around the agglomerated particles and the interaction of the particles with the substrate surfaces during dryness are important for the ordering. The microscopic drying patterns of gel spheres were quite different from those of linear type polymers and also from typical colloidal hard spheres, though the macroscopic patterns such as broad ring formation at the edges of the dried film were similar to each other.     

Drying dissipative structures of thermo-sensitive gel spheres of poly(N-isopropylacrylamide). Influence of degree of cross-linking of the gels

Drying dissipative patterns of de-ionized suspensions (colloidal crystal state above the critical concentrations of crystallization) of the thermo-sensitive gels of poly(N-isopropylacrylamide) with degrees of cross-linking of 10% and 2% (pNIPAm(200–10) and pNIPAm(200–2)) were observed at 20?°C and 45?°C on a cover glass, a watch glass, and a Petri glass dish. The broad rings were observed, and their size decreased as micro-gel concentration decreased. Formation of the monodispersed agglomerated particles and their ordered arrays were observed. Microscopic drying structures of (a) flickering ordered spoke-lines, (b) ordered rings, (c) net structure, and (d) lattice-like ordered structures of the agglomerated particles are observed. The net and lattice structures formed more favorably at high degrees of cross-linking, at high concentrations of the gels, and/or high temperatures. By the addition of sodium chloride, very large dendrite-like and net structures of the large agglomerated particles formed at 20?°C and 45?°C, respectively. Importance of the cooperated convectional flow of the agglomerated particles during the drying processes is supported for the ordered array formation. The role of the electrical double layers around the agglomerated particles and the interaction of the particles with the substrate surfaces during dryness are also important for the ordering. The microscopic drying patterns of gel spheres were different from those of linear type polymers and also from typical colloidal spheres, though the macroscopic patterns of gel system such as broad ring formation at the edges of the dried film were similar to other two systems.     

Drying dissipative structures of thermo-sensitive gel spheres of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) with low degree of cross-linking

Drying dissipative patterns of deionized suspensions (colloidal crystal state at high concentrations) of the thermo-sensitive gels of poly(N-isopropylacrylamide) with low degree of cross-linking of 0.5% (318 nm and 116 nm in the hydrodynamic diameter at 25 °C and 45 °C) were observed at 20 °C and 45 °C on a cover glass, a watch glass and a Petri glass dish. The broad rings were observed and their size decreased as micro-gel concentration decreased. Formation of the monodispersed agglomerated particles and their ordered arrays were observed. This work clarified the formation of the drying microscopic structures of (a) flickering ordered spoke-lines, (b) ordered rings, (c) net structure, and finally (d) lattice-like ordered structures of the agglomerated particles. The net and lattice structures formed more favorably at higher temperatures and/or higher degree of cross-linking of the gels. Importance of the convectional flow of the agglomerated particles during the drying processes is supported for the ordered array formation. The role of the electrical double layers around the agglomerated particles and the interaction of the particles with the substrate surfaces during dryness are also important for the ordering. The microscopic drying patterns of gel spheres were quite different from those of linear-type polymers and also from typical colloidal spheres, though the macroscopic patterns such as broad ring formation at the edges of the dried film were similar to each other.     

Drying dissipative structures of thermo-sensitive gel spheres of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide)

Drying dissipative patterns were observed at 25 °C, 33 °C, and 45 °C on a cover glass, a watch glass, and a Petri glass dish during the course of dryness of colloidal crystals of the thermo-sensitive gels of poly(N-isopropylacrylamide) (PNIPA). Two kinds of broad rings, i.e., transparent ring at the outside edge and the ring in the inner area from the edge, were observed. Sizes of the former were the same as those of the initial liquids irrespective of gel concentration, whereas sizes of the latter decreased as gel concentration decreased. These broad rings were composed mainly of the monomeric and the agglomerated gel particles, respectively. Formation of the monodispersed agglomerated particles and their ordered arrays in the inner area of the dried film were observed especially on a Petri glass dish and a watch glass. The important role of the electrical double layers formed around the agglomerated particles is supported for the ordering of the agglomerated particles. The essential differences in the drying patterns between PNIPA gel spheres and the typical colloidal particles did not appear.     

结构与制备条件对两亲性偶氮聚合物胶体球尺寸和光响应性的影响

合成了3种具有不同官能团或官能化度的双亲性多分散偶氮聚合物.系统研究了它们在选择性溶剂中形成聚合物胶体球时,各种因素对胶体球尺寸和光响应性能的影响规律.结果表明,不仅官能团和官能化度对胶体球的尺寸与光响应性有明显影响,具体的制备条件(如初始浓度、沉淀剂加入速率等)对胶体球尺寸和光响应性能也有重要影响.聚合物胶体球的粒径随官能化度的增加而增大;随初始浓度的增加和沉淀剂加入速率的减小而增大.聚合物PEAPE胶体球的光致异构化速率快于PCNPE胶体球的光致异构化速率.聚合物胶体球的光致异构化速率随官能化度的增加而减小;随初始浓度的增加和沉淀剂加入速率的减小而减小.这些影响表现出了明显的规律性.从双亲性聚合物在选择性溶剂中自组装形成胶体球的热力学与动力学因素出发,讨论了上述现象产生的原因.     

Formation of highly monodispersed emulsifier-free cationic poly(methylstyrene) latex particles

Highly monodispersed emulsifier-free poly(methylstyrene) (PMS) latex particles were prepared via an emulsifier-free emulsion polymerization in the presence of 2,2′-azobis-(2-amidineopropane) dihydrochloride (V-50) as an initiator. A combination of kinetics and molecular weight distribution studies revealed that the polymerization followed the micellization nucleation mechanism. Results showed that an appropriate initiator concentration was necessary to obtain monodisperse and stable latex particles. Conversion of methylstyrene was found to increase significantly with increasing initiator concentrations. However, the size of PMS latex particles decreased with both the increase of initiator concentration and the reaction temperature at a constant ionic strength. The particle size was increased as the ionic strength of the aqueous phase increased, yet the variation of ionic strength had little effect on the particle size distribution. SEM micrographs showed that an agitation rate of 350 rpm or higher was required in order to produce highly monodispersed poly(methylstyrene) latex particles. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2069–2074, 1999     

Direct-write fabrication of colloidal photonic crystal microarrays by ink-jet printing

An array of the colloidal photonic crystals was directly fabricated using an ink-jet printing. The colloidal ink droplets containing the monodispersed polystyrene latex particles were selectively deposited on a hydrophobic surface. Solvent evaporation from each ink droplet leads to a formation of microdome-shaped colloidal assembles of close-packed structures. Microspectroscopic analysis has confirmed that the individual assembly serves as a photonic crystal and its optical properties can be correlated with the microstructural features. Unlike other techniques of patterned growth of colloidal photonic crystal, the substrate does not need to be patterned first and no template is needed in the direct writing by the ink-jet printing. Using our strategy, we have rapidly produced the colloidal photonic crystal microarrays composed of different-sized spheres addressably patterned on the same substrate.     

单分散聚苯乙烯乳胶有序膜在二氧化硅多孔材料制备中的模板作用

自然界中许多物质经千万年发展进化,具有特殊结构,决定了它们具有奇异特性.人们对此过程非常关注,试图了解其结构性能关系,从而实现人工合成,仿生学应此而产生.比如天然蛋白石能呈现出鲜艳颜色,其原因在于单分散二氧化硅微球与具有选择性吸收光的某些金属氧化物微粒形成了有序的超晶格结构[1].为了模拟此过程,人们以单分散二氧化硅或聚苯乙烯微粒形成的胶体晶作为模板,实现蛋白石的人工合成[2].可以说,模板合成技术是制备有序材料的有效手段.本文以单分散聚苯乙烯乳胶室温形成的有序膜为模板,采用快速溶胶凝胶方法,制备了聚苯乙烯/二氧化硅…     

Drying dissipative structures of lightly cross-linked poly(2-vinyl pyridine) cationic gel spheres stabilized with poly(ethylene glycol) in the deionized aqueous suspension

Drying dissipative patterns of deionized and colloidal crystal-state suspensions of the cationic gel spheres of lightly cross-linked poly(2-vinyl pyridine) stabilized with poly(ethylene glycol) were observed on a cover glass, a watch glass, and a Petri glass dish. Convectional patterns were recognized with the naked eyes. The broad rings were observed in the drying pattern and their size and width decreased as gel concentration decreased. Formation of the monodispersed agglomerated particles and their ordered arrays were observed. This work clarified the formation of the drying microscopic structures of (a) ordered rings, (b) flickering ordered spoke-lines, (c) net structure, and (d) lattice-like ordered structures of the agglomerated particles. The ordering of the agglomerated particles of the cationic gel spheres is similar to that of the anionic thermo-sensitive gel spheres of poly(N-isopropyl acrylamide). The role of the electrical double layers around the agglomerated particles and the interaction of the particles with the substrates during dryness are important for the ordering. The microscopic drying patterns of gel spheres were different from those of linear-type polymers and also from typical colloidal hard spheres, though the macroscopic patterns such as broad ring formation at the edges were similar to each other. The addition of sodium chloride shifted the microscopic patterns from lattice to net structures.     

Colloidal crystallization of thermo-sensitive gel spheres of poly (N-isopropyl acrylamide). Influence of degree of cross-linking of the gels

Morphology, phase diagram, and reflection spectroscopy of the colloidal crystals of thermo-sensitive gel spheres, poly (N-isopropylacrylamide) having degrees of cross-linking 10 and 2?mol.% (pNIPAm(200?C10) and pNIPAm(200?C2)) were studied. Giant colloidal single crystals formed at very low gel concentrations. Critical concentrations of melting increased as the degree of cross-linking decreased in the range from 10 to 0.5?mol.% and/or suspension temperature increased from 20 to 45?°C. The critical concentration decreased sharply as the suspensions were deionized with coexistence of the mixtures of cation- and anion-exchange resins. Density of a gel sphere (gel concentration in weight percent divided by that in volume percent) increased sharply as the degree of cross-linking and/or temperature increased. These results demonstrated that the colloidal crystallization takes place by the extended electrical double layers formed around the gel spheres in addition of the excluded-volume effect of the gels. Most of the researchers including the authors have believed that the crystallization of the gel spheres takes place by the excluded-volume effect. However, the present work clarified that the colloidal interfaces, which are inevitable for the formation of the electrical double layers, are formed firmly between the water phase and gel spheres, though the gel spheres contain a lot of water molecules in the sphere region.     

MMA-EA-AA无皂乳液聚合中粒径及粒径分布的控制

系统研究了MMA EA AA三元无皂乳液聚合体系中各种因素对乳胶粒大小及分布的影响 ,制得了单分散、粒径在 30 0～ 6 0 0nm可控聚合物乳胶粒 .结果表明 ,在过硫酸铵用量一定的条件下 ,聚合初期加入大量引发剂可同时提高单体转化率和乳胶粒的单分散性 ;随着引发剂和AA用量的增加以及聚合温度的升高 ,胶粒粒径逐渐减小 ,转化率逐渐升高 ;随着NH4 HCO3用量的增加 ,粒径逐渐增大 ,当NH4 HCO3用量达到 0 5g以后 ,转化率逐渐降低 ;搅拌速率为 30 0r min左右时 ,单体转化率最高 ,所得乳胶粒粒径最均一 .     

Viscosity measurements of water at high temperatures and pressures using dynamic light scattering

The application of dynamic light scattering to measure viscosity of water at high temperatures and pressures is demonstrated. Viscosity was obtained from the translational diffusion coefficient of probe particles dispersed in the medium by the Einstein-Stokes relationship. Measurements were carried out with polystyrene latex, colloidal silica, and colloidal gold. Under a constant pressure of 25 MPa, good agreement was found between the measured and calculated viscosities up to 275 degrees C with the polystyrene latex, 200 degrees C with the colloidal silica, and 297 degrees C with the colloidal gold. It was found that failure of the measurements at high temperatures is ascribed to change in either the dispersion stability or chemical stability of the probe particles. The present results indicate that the technique could also be used for other supercritical fluids having high critical temperature and pressure, such as methanol (T(c) = 239.4 degrees C, P(c) = 8.1 MPa) and ethanol (T(c) = 243.1 degrees C, P(c) = 6.4 MPa).     

Determination of Volatile Nitrosamines in Latex Products by HS-SPME�CGC�CMS

Nitrosamines which have been detected in various latex products are carcinogens. The method for determination of volatile nitrosamines in latex products was developed using a combination of headspace solid phase micro-extraction (HS-SPME) and gas chromatography?Cmass spectrometry (GC?CMS). A carboxen/polydimethylsiloxane (CAR/PDMS) fiber was used for HS-SPME involving the following variables: (1) agitation conditions, (2) extraction temperature (3) extraction time, and (4) salt concentration. The instrument performances of three detection systems including GC combined thermal energy analyzer, nitrogen chemiluminescence detector and MS were evaluated. The agitation conditions including magnetic stirring and ultrasonication were investigated by the comparison of extraction efficiency of HS-SPME for nitrosamines. Obtained optimal detection conditions of nitrosamines were HS-SPME at 45 °C for 60 min assisted with magnetic stirring and saturated NaCl followed by GC?CMS. To evaluate this method performance, the commercial products including eleven latex products (gloves, balloons and condoms) and four liquid silicone nipples were analyzed with the method. The results revealed that the method is suitable for simple and effective determination of nitrosamines in latex products. The advantage of this HS-SPME?CGC?CMS method is simple treatment, fast analysis, adequate sensitivity and without organic solvent.     

Kinetic studies of colloidal crystallization of thermo-sensitive gel spheres of poly(N-isopropylacrylamide)

Crystal growth rate coefficients, k of the colloidal crystallization of thermo-sensitive gel spheres of poly(N-isopropylacrylamide) were measured from the time-resolved reflection spectroscopy mainly by the inverted mixing method in the deionized state. Crystallization of colloidal silica spheres were also measured for comparison. The k values of gel and silica systems increased sharply as the sphere concentration and suspension temperature increased. The k values of gel system were insensitive to the degree of cross-linking in the range from 10 to 2?mol% of cross-linker against amount of the monomer in mole and decreased sharply when the degree of cross-linking decreased further to 0.5?%. The k values increased as gel size increased. The k values of gel systems at 20?°C were small and observed only at the very high sphere concentration in volume fraction, whereas those at 45?°C were high but smaller than those of silica systems. Induction time (t _i) after which crystallization starts, increased as the degree of cross-linking increased and/or the gel size decreased at any temperatures, when comparison was made at the same gel concentration. The t _i values at 45?°C were high and decreased sharply with increasing sphere concentration, whereas those at 20?°C were high only at the very high sphere concentrations. Significant difference in the k and t _i values between the soft gels and hard silica spheres was clarified. These kinetic results support that the electrical double layers play an important role for the gel crystallization in addition to the excluded volume of gel spheres. It is deduced further that the electrical double layers of the gel system form from the vague interfaces (between soft gel and water phases) compared with those of typical colloidal hard sphere system.     

Polyaniline dispersions 7. Dynamic light scattering study of particle formation

 When aniline is oxidized in the presence of colloidal silica, composite polyaniline–silica particles of submicrometer size are obtained. Dynamic light scattering was used to monitor the course of dispersion polymerization of aniline and the formation of particles. The increase of a hydrodynamic radius of particles was observed as polyaniline had been produced. Additional increase in particle size after polymerization has also been recorded. The rate of aniline polymerization was found to increase with increasing temperature in the range 0–50 °C. Well-defined particles are formed below 30 °C while above this temperature the colloidal stability of the resulting systems is limited. The activation energy of aniline polymerization was estimated. Received: 24 February 1997 Accepted: 7 May 1997     

Effects of liquid bridge between colloidal spheres and evaporation temperature on fabrication of colloidal multilayers

For the application of colloidal crystal films as "photonic band gap" materials, their domain size and thickness are significant. The substrate withdrawing speed, the colloidal suspension volume fraction, and the colloidal suspension temperature have been studied for the domain size and thickness controls of colloidal crystals in this study. Stable dispersions of monodispersed polystyrene spheres with a diameter of 245 nm were synthesized according to a general emulsion polymerization for colloidal crystal films. By experimental results and the theoretical relationship between the number of layers and other parameters, we could know that the water bridge between colloidal spheres (which is formed by capillary force) influences the number of colloidal crystal layers significantly.     

SiO2胶体颗粒的三维有序自组装

由SiO2胶体颗粒的三维有序自组装可以得到面心立方三维结构,它具有折射率周期性变化的特点。它的制备涉及胶体化学、材料科学等学科的前沿领域。其自组装方法包括胶体颗粒的沉降自组装、胶体颗粒在物体限制下的自组装、胶体颗粒的连续对流自组装和利用胶体颗粒表面电性质的自组装。本文对这些组装方法进行了介绍。     

Facile fabrication of mechanochromic-responsive colloidal crystal films

This paper presents a simple approach to fabricate a reversible mechanochromic-responsive crystal film based on the room-temperature film-formation of monodisperse polymer latex by the aid of nanosilica particles. In this approach, when the "soft" colloidal polymer spheres were blended with colloidal silica particles and then cast on a substrate, followed by drying at room temperature for self-assembly, an elastic crystal film was directly obtained. This crystal film has not only reversible and repeatable mechanochromic-responsive property, but also tunable color and peak position covering almost entire visible spectral region, depending upon the sizes of polymer spheres and strains. This optical response is attributed to the variation of lattice spacing during deformation.     

Effect of the structure of latex particles on adhesion. Part I: Synthesis and characterization of structured latex particles of acrylic copolymers and their peel adhesion behavior

This is a series of articles that deals with fundamental aspects of the effects of the structure of latex particles of acrylic copolymers on their adhesion behavior. Specifically, relationship or analogy between rheological properties and adhesion performance of the acrylic copolymers was demonstrated. The first part of this series concerns the synthesis and characterization of latex particles with desired structures and compositions, and the experimental results of peel adhesion. The second part develops an analogy between the peel adhesion performance of the adhesives and rheological properties of the corresponding copolymers. The third part addresses the generalities and particularities of three major tests for adhesion: peeling, blistering, and spontaneous peeling. Three types of structured latex particles were synthesized by three different emulsion polymerization processes: the first type had a uniform composition over the entire particles with a glass transition temperature (T_g) varying between ?40°C and 0°C, depending upon the compositions of monomers involved in the copolymer; the second type was of core-shell structure. As for the third type, the composition of monomers varied gradually across the particle radii. The glass transition behavior and the dynamic mechanical properties in the solid state of the copolymers confirmed the structures of the corresponding latex particles. On the other hand, the peel adhesion performance of the films of these latex particles varied with the dynamic mechanical properties of the corresponding copolymers. This implies that a correlation could be found between the structure of the latex particles, dynamic mechanical properties in the solid state of the corresponding copolymers, and the peel adhesion performance of the adhesive films. ©1995 John Wiley & Sons, Inc.