Structured latex particles

Abad C, De La Cal J.C, Asua J.M (1995) Core-shell Structured Latex Particles. IE. Structure-properties Relationship in Toughening of Polycarbonate with Poly(M-butyl acrylate)/Poly(benzyl methacrylate-styrene) Structured Latex Particles. J. Appl. Polym. Sci. 56 419-455. 

Progress in Organic Coatings 35, No.l, Aug.1999, p.265-75 STRUCTURED LATEX PARTICLES WITH IMPROVED MECHANICAL PROPERTIES... 

No.4, 24th Feb. 1997, p. 1028-32 EFFECTS OF CROSSLINKING ON THE MORPHOLOGY OF STRUCTURED LATEX PARTICLES. II. EXPERIMENTAL EVIDENCE FOR LIGHTLY CROSSLINKED SYSTEMS Durant Y G Sundberg E J Sundberg D C New Hampshire,University... 

Journal of Applied Polymer Science 64, No.6,9lh May 1997, p.1123-34 PREPARATION AND CHARACTERISATION OF SBR AN STRUCTURED LATEX PARTICLES... 

In all of these applications the particles are soft and must be capable of forming a film at temperatures close to room temperature. In addition, they must display favorable interactions with the surface of the substrate on which they are applied. In this respect, a review of recent publications and patents showed that structured latex particles still represent an active area of research, the principal objective being to improve the performances of the coating formulation. Indeed, as will be illustrated below in the case of organic/inorganic colloids, structured latexes represent a possible means to overcome the usual compromises between a good film quality and optimal properties. 

Shaffer et al [365] have continued to modify staining techniques for TEM of latex particles. Recent work on structured latex particles prepared by seeded emulsion polymerization focused on the effects of changes in polymerization variables, such as batch versus semicontinuous, core-shell ratio, shell thickness and shell composition. In this system the core was poly(n-butyl acrylate) and the shell was poly(benzyl methacrylate-styrene). A few drops of the latex was combined with a few drops of a 2% uranyl acetate solution which serves as a negative stain. A drop of that mixture was deposited on a stainless steel formvar-coated grid. After drying it was stained in ruthenium tetroxide vapor to differentiate the rubbery core, which is not... 

FIG. 39 Various structures obtained by drying of particle monolayers (a) the two-dimensional liquid-solid interface (latex particles/mica) (b) the caterpillar structure (latex particle/mica) (c) the labyrinth structure (melamine latex particles/mica). 

Before the investigation of any targeted biomedical diagnostic application, several aspects related to colloidal particles should be addressed starting basically from particle size, size distribution, surface polarity, and also intrinsic properties. Consequently, the synthesis process should be well adapted in order to prepare structured latex particles bearing a reactive shell with well-defined properties. The colloidal particles are not only under evaluation or being used as a model in various biomedical applications, but actually are in use in different capacities for various biomedical applications. Some examples are as follows ... 

The progression of an ideal emulsion polymerization is considered in three different intervals after forming primary radicals and low-molecular weight oligomers within the water phase. In the first stage (Interval I), the polymerization progresses within the micelle structure. The oligomeric radicals react with the individual monomer molecules within the micelles to form short polymer chains with an ion radical on one end. This leads to the formation of a new phase (i.e., polymer latex particles swollen with the monomer) in the polymerization medium. 

The function of emulsifier in the emulsion polymerization process may be summarized as follows [45] (1) the insolubilized part of the monomer is dispersed and stabilized within the water phase in the form of fine droplets, (2) a part of monomer is taken into the micel structure by solubilization, (3) the forming latex particles are protected from the coagulation by the adsorption of monomer onto the surface of the particles, (4) the emulsifier makes it easier the solubilize the oligomeric chains within the micelles, (5) the emulsifier catalyzes the initiation reaction, and (6) it may act as a transfer agent or retarder leading to chemical binding of emulsifier molecules to the polymer. 

The dispersion polymerization of alkylcyanoacry-lates provides degradable uniform polyalkylcyanoacry-late latex particles in submicron size range. These particles are termed as biodegradable nanoparticles in the common literature [102-107]. The general structure of alkylcyanoacrylates is ... 

This paper presents the physical mechanism and the structure of a comprehensive dynamic Emulsion Polymerization Model (EPM). EPM combines the theory of coagulative nucleation of homogeneously nucleated precursors with detailed species material and energy balances to calculate the time evolution of the concentration, size, and colloidal characteristics of latex particles, the monomer conversions, the copolymer composition, and molecular weight in an emulsion system. The capabilities of EPM are demonstrated by comparisons of its predictions with experimental data from the literature covering styrene and styrene/methyl methacrylate polymerizations. EPM can successfully simulate continuous and batch reactors over a wide range of initiator and added surfactant concentrations. 

In the same year, Fulda and Tieke [75] reported on Langmuir films of monodisperse, 0.5-pm spherical polymer particles with hydrophobic polystyrene cores and hydrophilic shells containing polyacrylic acid or polyacrylamide. Measurement of ir-A curves and scanning electron microscopy (SEM) were used to determine the structure of the monolayers. In subsequent work, Fulda et al. [76] studied a variety of particles with different hydrophilic shells for their ability to form Langmuir films. Fulda and Tieke [77] investigated the influence of subphase conditions (pH, ionic strength) on monolayer formation of cationic and anionic particles as well as the structure of films made from bidisperse mixtures of anionic latex particles. 

In 1997, a Chinese research group [78] used the colloidal solution of 70-nm-sized carboxylated latex particles as a subphase and spread mixtures of cationic and other surfactants at the air-solution interface. If the pH was sufficiently low (1.5-3.0), the electrostatic interaction between the polar headgroups of the monolayer and the surface groups of the latex particles was strong enough to attract the latex to the surface. A fairly densely packed array of particles could be obtained if a 2 1 mixture of octadecylamine and stearic acid was spread at the interface. The particle films could be transferred onto solid substrates using the LB technique. The structure was studied using transmission electron microscopy. 

Fulda and Tieke [77] studied the effect of a bidisperse-size distribution of latex particles on the structure of the resulting LB monolayer. For this purpose, a mixed colloidal solution of particles la and lb was spread at the air-water interface. Particles la had a diameter of 434 nm, particles lb of 214 nm. The monolayer was compressed, transferred onto a solid substrate, and viewed in a scanning electron microscope (SEM). In Figure 10, SEM pictures of LB layers obtained from various bidisperse mixtures are shown. 

Fulda and coworkers [92,93], Bliznyuk and Tsukruk [94], and Serizawa and coworkers [95-97] were the first who tried to use this technique for the preparation of ordered bi- and multilayer assemblies of oppositely charged latex particles. The structure was investigated using scanning force microscopy (SFM) and SEM. In a further publication, Kampes and Tieke [98] studied the influence of the preparation conditions on the state of order of the monolayers. In the following section, the recent studies are more extensively reviewed. 

Polymeric particles can be constructed from a number of different monomers or copolymer combinations. Some of the more common ones include polystyrene (traditional latex particles), poly(styrene/divinylbenzene) copolymers, poly(styrene/acrylate) copolymers, polymethylmethacrylate (PMMA), poly(hydroxyethyl methacrylate) (pHEMA), poly(vinyltoluene), poly(styrene/butadiene) copolymers, and poly(styrene/vinyltoluene) copolymers. In addition, by mixing into the polymerization reaction combinations of functional monomers, one can create reactive or functional groups on the particle surface for subsequent coupling to affinity ligands. One example of this is a poly(styrene/acrylate) copolymer particle, which creates carboxylate groups within the polymer structure, the number of which is dependent on the ratio of monomers used in the polymerization process. 

The influence of the surfactant in the modified polymers of Figure 1 on n (aqueous solutions, Table I) is not overpowering. The surfactant s influence is diminished by the amphiphilic oxyethylene units which lie interfacially flat at the aqueous-air interface. The hydrophobes are structurally similar to the surfactants providing stability to commercial latices and should be capable of competing with the classical surfactants at the latex surface, but this ability is not reflected in 7T values. The oxyethylene units have been demonstrated(18) to provide osmotic stabilization to latex particles. 

The surfaces of colloidal particles are often charged and these changes can arise from a number of sources. Chemically bound ionogenic species may be found on the surface of particles such as rubber or paint latex particles. Charged species may be physically adsorbed if ionic surface active materials, for example, have been added. A charged surface may occur on a crystal lattice. An example is the isomorphous substitution of lower valency cations such as aluminium for silicon in the lattice structure of clays. A further example is the adsorption of lattice ions... 

O. Velev, K. Furusawa, and K. Nagayama Assembly of Latex Particles by Using Emulsion Droplets as Templates. . Micro structured Hollow Spheres. Langmuir 12, 2374 (1996). 

FIG. 13.4 Stereo pairs of colloidal dispersions generated using computer simulations, (a) Polystyrene latex particles at a volume fraction of 0.13 with a surface potential of 50 mV. The 1 1 electrolyte concentration is 10 7 mol/cm3. The structure shown is near crystallization. (The solid-black and solid-gray particles are in the back and in the front, respectively, in the three-dimensional view.) (b) A small increase in the surface potential changes the structure to face-centered cubic crystals. (Redrawn with permission from Hunter 1989.)... 

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