We report the formation of novel self-assembled ultrathin (ca. 20 nm) films comprising in-plane arrays of nanoscale surface cavities. The original micellar thin films, formed by casting kinetically stable reverse micelles from a solution of a styrene (PS)−acrylic acid (PAA) diblock copolymer in toluene onto silicon nitride substrates, consist of lateral hexagonal arrays of spherical PAA microdomains in PS matrix. Upon aqueous treatment to load metal ions into the PAA domains, cavitation of the individual PAA micelle cores occurs, leading to the formation of cavities in the center of the micelles and exposing the PAA domains to the film's surface. Experimental evidence reveals that cavitation takes place as a result of hydration and swelling of the PAA micelle cores during sample treatment in an alkaline solution. The use of these cavitated, metal-loaded PAA domains as arrays of open nanoreactors for inorganic nanocluster synthesis is demonstrated.

Cavitated block copolymer micellar thin films: Lateral arrays of open nanoreactors

This invention relates to a process of making hollow polymer latex particles without the use of acid in the swellable polymer core; the latexes are useful as opacifying plastic pigments for various coatings and particularly as gloss-enhancing plastic pigments for paper and paperboard coatings. Known methods for preparing hollow latexes require cores containing acid or acidic monomers to enable swelling to core at room temperature. The existence of acid in the polymer disadvantageously increases the polymer's affinity to water. Applicants have discovered that non-carboxylated latexes having a variety of T g 's will also swell at higher temperatures. The mechanism entails the use of acrylate and methacrylate ester monomers which are hydrolyzable and swellable at higher temperatures in alkaline environments. Such mechanisms for making swollen latexes provide for a wide variety of potential end-uses as well as a wide variety of potential latexes.

Process of making hollow polymer latex particles

Rheological techniques are used to probe the behavior of hydrophobic alkali-swellable emulsion (HASE) polymers, bearing n-alkyl hydrophobes, in aqueous alkaline media. The polymers possess a comb-like architecture with a polyelectrolyte backbone (ethyl acrylate-co-methacrylic acid) and hydrophobes (∼16 per polymer chain) tethered to the backbone via polyether side chains. The size of the hydrophobes is varied from n-C8 to n-C20 in this study. It is shown that, at such a level of hydrophobic modification, and at relatively high polymer concentrations, the microstructure in these polymer systems is akin to that existing in concentrated microgels. Thus, the original polymer latex particles swell extensively in alkaline media and disintegrate to form a system of close-packed, compressible (“soft”) aggregates. This is reflected in the rheological response of the system where we observe a high steady shear viscosity with no zero-shear plateau at low shear rates followed by considerable shear thinning and, a characteristic power-law behavior (G′, G″∼ω0.4) under oscillatory shear persisting over a broad range of time scales. Concentration-independent master curves are obtained for the storage modulus, G′, with the level of G′ increasing with hydrophobe size. The similarity in the dynamic response suggests that there exists a qualitative equivalence in microstructure over the range of systems, the only difference being the “softness” or compressibility of the particles. Data from this study are also contrasted with those for a similar HASE polymer bearing a smaller number of alkylaryl hydrophobes [J. Rheol. 41, 427–444 (1997)]. In the latter case, the rheology can be interpreted in terms of hydrophobic associations and chain entanglements occurring in solution. Thus, subtle variations in molecular architecture are shown to cause significant differences in morphology and microstructure for these polymer systems.Rheological techniques are used to probe the behavior of hydrophobic alkali-swellable emulsion (HASE) polymers, bearing n-alkyl hydrophobes, in aqueous alkaline media. The polymers possess a comb-like architecture with a polyelectrolyte backbone (ethyl acrylate-co-methacrylic acid) and hydrophobes (∼16 per polymer chain) tethered to the backbone via polyether side chains. The size of the hydrophobes is varied from n-C8 to n-C20 in this study. It is shown that, at such a level of hydrophobic modification, and at relatively high polymer concentrations, the microstructure in these polymer systems is akin to that existing in concentrated microgels. Thus, the original polymer latex particles swell extensively in alkaline media and disintegrate to form a system of close-packed, compressible (“soft”) aggregates. This is reflected in the rheological response of the system where we observe a high steady shear viscosity with no zero-shear plateau at low shear rates followed by considerable shear thinning and, a cha...

/pdf/associative-polymers-bearing-n-alkyl-hydrophobes-rheological-4atfyw9tla.pdf

Associative polymers bearing n-alkyl hydrophobes: Rheological evidence for microgel-like behavior

Hollow-particle latexes were prepared according to the following stages: (1) the preparation of the methyl methacrylate–methacrylic acid (MAA)–ethylene glycol dimethacrylate copolymer (I) latex, (2) the preparation of a shell (II) based on polystyrene or styrene–acrylonitrile–divinyl benzene copolymer polymerized onto copolymer (I) particles, and (3) the neutralization of the core (I) carboxyl groups with a base (NH4OH or NaOH) at temperatures close to the glass-transition temperature of the polymer (II). The neutralization resulted in the expansion of the particles and formed water-filled hollow particles. The microspheres had an overall diameter of 460–650 nm and a hollow diameter of 300–450 nm. Rheological studies and particle size measurements by transmission electron microscopy and dynamic light scattering of the copolymer (I) latex indicate that the maximum particle swelling occurred at an approximately equimolar MAA/base ratio. It was found that even without the neutralization of the MAA units, a small hollow formation in the latex particles occurred during stage 2 because one volume of the copolymer (I) retained about 8 volume parts of water. It was also discovered that the final hollow-particle geometry after neutralization depends on the shell copolymer thickness and type as well as on the conditions during stage 3, that is, the time, temperature, base type, and concentration. The opacifying ability of the synthesized hollow particles was investigated in latex coatings. The opacifying ability values were generally in agreement with the hollow-particle geometry. The only exception was related to the copolymer (I)/copolymer (II) ratio. The maximum hollow volume was obtained at this value equal to 1/8, whereas the highest opacifying ability was observed at 1/10. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1435–1449, 2001

Hollow‐particle latexes: Preparation and properties

Microstructure and rheology of stimuli-responsive microgel systems--effect of cross-linked density.

Viscosity-versus-pH relationships for a large number of methacrylic acid-containing emulsion polymers have been measured. The monomers chosen for this study were so selected because they represent synthesized latexes of high and low Tg and comparative hydrophilicity. These were styrene, methyl methacrylate, ethyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate. The postulated mechanism involved in the transition from an unneutralized latex particle to the neutralized species is accounted for in terms of varying degrees of particle swelling. In the limiting case, particle swelling is followed by complete solution of the polymer. The most important variables are the per cent methacrylic acid and the polymer Tg and hydrophilicity as determined by the comonomers present. The degree of particle swelling ranges from none for high styrene-containing latexes to high degrees of swelling followed by polymer solubilization for high ethyl acrylate-containing latexes.

Mechanism of alkali thickening of acid-containing emulsion polymers. I. Examination of latexes by means of viscosity

The mechanism of alkali thickening of acid-containing emulsion polymers has been confirmed by visual examination of the swelling and disappearance of latex particles with the light microscope Specially prepared large particle-sized latexes were used in this study Each latex was examined from 0%–200% neutralization with base The particle swelling and dissolution behavior correlated with viscosity measurements, high viscosity being present for swollen particle systems and low viscosity for true solutions The neutralized state of all acid-containing latexes can be pictured in a cube with the important variables being per cent acid, hydrophilicity of the comonomers, and Tg At the bottom will be latexes only slightly affected by neutralization, above this will be a swollen particle zone, and the largest area will be a true solution zone The true solution zone will be enlarged by lowering the molecular weight of the latex polymer

C. J. Verbrugge

Papers

Mechanism of alkali thickening of acid-containing emulsion polymers. I. Examination of latexes by means of viscosity

Mechanism of alkali‐thickening of acid‐containing emulsion polymers. II. Examination of latexes with the light microscope