Stability Of Latex Research Articles

Electrophoretic mobility evidence of surfactant partitioning in a waterborne latex

In order to enhance substrate adhesion and pigment dispersion of fluorinated polymers, polyvinylidene fluoride (PVDF) type fluoropolymers are often used in combination with certain amounts of acrylics in paint formulations. We prepared an acrylic modified fluoropolymer (AMF) [1] latex by emulsion polymerization and monitored the effect of the addition of typical coalescents (TEX, DPM, DGB, and EGB) on the stability of an AMF latex. Both the effect on the bare latex and on surfactant post-added latex were investigated. No particular effect was noticed on the bare latex itself, but when surfactant is adsorbed initially to the particle surface, we observed surfactant partitioning between the polymer interface and the water phase, with different partitioning ratios depending on the coalescing solvent type. This leads to the presence of labile peaks in the electrophoretic mobility spectra and possible surfactant desorption from the AMF surface, with consequent latex destabilization.

On the colloidal stability of polystyrene particles prepared with surface-active initiators

The stability of polystyrene latexes prepared with 2,2′-azobis( N-2′-methylpropanoyl-2-amino-alkyl-1)-sulphonates as surface-active initiators (inisurfs) in emulsion polymerization is investigated. The experimentally observed stability during emulsifier-free emulsion polymerization depends on the alkyl chain length of the inisurfs. The calculated barrier height of the overall interaction energy fits nicely with the experimentally observed stability during the polymerization.

Synthesis and characterization of amphoteric latex particles

Stable monodisperse amphoteric latex particles were prepared by the semibatch surfactant-free emulsion copolymerization of methyl methacrylate and methacrylic acid (MAA) initiated by 2,2′-azobis(2-amidinopropane) dihydrochloride (V-50). These submicron particles have a net positive charge, which is attributed to the ionized amino group at low pH. In contrast, they become negatively charged owing to the ionized carboxyl group at high pH. There exists a pH at which these particles exhibit a net charge of zero (pI). At a constant level of V-50, the pI value of these latices decreases with increasing amount of MAA used in the polymerization recipe. The effect of pH on the colloidal stability of these amphoteric latices toward the addition of the negatively charged latex was investigated. The resultant coagulation kinetics was used to study the electrostatic interaction between the amphoteric particles and negatively charged particles.

Study of the colloidal stability of an amphoteric latex

We have studied the colloidal stability of an amphoteric latex (–COOH and NH2 surface groups) with a low-angle light scattering technique (nephelometry). Measurements were carried out at different pH values and electrolyte concentrations (NaCl or CaCl2). The results show a behaviour in agreement with DLVO theory when the pH of the medium is below the isoelectric point (i.e.p.) of the latex: at low ionic strengths the latex is stable, but it becomes completely unstable and coagulates when electrolyte concentration goes over a particular value (the critical coagulation concentration). However, when pH is raised above the isoelectric point, the latex is completely stable even at high electrolyte concentrations, showing a behaviour clearly opposite to the theory. This could be explained by means of an additional short-range repulsive "hydration force" due to the structure of water molecules that accompany hydrated cations around the hydrophilic latex surface. The morphology and electrical properties of the latex surface have been studied by different methods: dynamic light scattering, electrophoretic mobility, potentiometric and conductometric titrations.

Synthesis and Rheological Properties of Some Styrene/Methacrylate Copolymer Latices

Copolymer emulsion latices based on styrene (St) with each of butyl acrylate (St/BuA), butyl methacrylate (St/BuMA), methyl methacrylate (St/MMA), and glycidyl methacrylate (St/GMA), were synthesized with different composition ratios (10/0, 7/3, 5/5, and 3/7) using potassium persulfate/sodium metabisulfite (KPS/NaMBS) as redox initiation system in the presence of a coemulsifier that consists of dodecyl benzene sodium sulfonate with polyvinyl alcohol (DBSS/PVA) and DBBS with polyoxyethylene glycol monomethyl ether (DBBS/POE). The obtained latices were characterized by 1H NMR and rheological and morphological techniques. The rheological features for the obtained latices are strongly dependent on the type of the monomer used. The viscosity measurements showed that all latices behave as a non‐Newtonian shear thinning (pseudoplastic). In addition, increasing the styrene ratio increases the apparent viscosity, pseudoplastic, and Bingham yield stress. The creep analysis for the latices demonstrated that the prepared latex using (DBSS/PVA) as a coemulsifier shows the least synersis effect than that obtained by using (DBSS/POE). Moreover, decreasing styrene content in the composition ratio improves the storage stability of copolymer latex. The morphological characteristics of the obtained latices clarify that the latex particles prepared in the presence of (DBSS/POE) as coemulsifier have the highest average volume particle diameter (D¯ v ) compared to that obtained for the latex prepared in the presence of (DBSS/PVA).

Stability of Dispersions of Fluorine-Containing Latexes and Its Effect on the Properties of Forming Films

The stability of latexes of poly(1,1-dihydroperfluoroheptyl acrylate) (LFM-3), poly(vinyl chloride-co-vinylidene chloride) (SVKh), poly(butadiene-co-methacrylic acid) (SKD-1), and their mixtures, as well as the wettability of the films produced on their basis are studied. It is revealed that, in some cases, the stability of binary systems exceeds that of individual dispersions. A correlation is established between the stability of latexes (varying in the film-formation process) and the critical concentration of their coagulation, on the one hand, and the water contact angles, on the other hand. It is shown that the aggregation of latex particles considerably affects the texture of hydrophobic films.

Successful Use of RAFT Techniques in Seeded Emulsion Polymerization of Styrene: Living Character, RAFT Agent Transport, and Rate of Polymerization

Reversible addition−fragmentation chain transfer (RAFT) polymerization techniques are successfully used to control molecular weight and polydispersity in the seeded emulsion polymerization of styrene. A novel technique was used to assist the transport into the seed particles of a RAFT agent that is of very low water solubility, ensuring the RAFT agent was localized in the particle phase. The polymer produced in these experiments was seen to have low molecular weight polydispersity (1.1 < Mw/Mn < 1.4), and the molecular weight could be controlled by the amount of RAFT agent used. The procedure permitted living polymerization to be performed in an emulsion polymerization system. Importantly, the RAFT agent had no adverse effect on latex stability, and unusual amounts of coagulum were not observed. Reductions in the rate of polymerization (measured by dilatometry) were observed along with significant inhibition periods, for which possible explanations and remedies are discussed. This appears to be the firs...

High solids content emulsions. II. Preparation of seed latices

The preparation of concentrated seed latices for use in bimodal and trimodal formulations is presented in the current work. Various recipes of surfactant and initiator were tested in order to allow us to control the number of particles produced during the nucleation stage. Following this, a semi-batch feed recipe that combined the use of oil-soluble initiators and pre-emulsified monomer was used to produce well-defined latices having well defined particle size distributions. It was found that the primary concern in maintaining latex stability and favorable viscosity was the reduction of undesirable secondary nucleation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1897–1915, 2002; DOI 10.1002/app.10512

Polymerization of high‐solids‐content acrylic latexes using a nonionic polymerizable surfactant

AbstractStable high‐solids‐content methyl methacrylate/butylacrylate latexes with small particle sizes (in the range of 150–180 nm) were obtained with a nonionic polymerizable surfactant (surfmer). Three percent of surfmer with respect to monomer was proven to be enough for the stabilization of the latexes. The influence of different operational variables on the stabilization of the final latex was analyzed, and the conditions needed to obtain coagulum‐free latex were assessed. The inorganic potassium persulfate/sodium metabisulfite initiator system provided better stability than the organic tert‐butyl hydroperoxide/ascorbic acid as a result of the end groups. In addition, the feeding of acrylic acid during the second half of the polymerization improved the stability of the final latex. The reduction of the feeding time was effective in the stabilization. Proof of the surfmer incorporation into the particles is presented. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1552–1559, 2002

High solids content emulsions. III. Synthesis of concentrated latices by classic emulsion polymerization

AbstractTwo different methods of producing bi‐ and trimodal latices of a mixture of methyl methacrylate, butyl acrylate, and small amounts of acrylic acid were tested. It is shown that a combination of concentrating blends of seed particles by semibatch reaction, followed by a nucleation of small particles plus a second semibatch phase allowed us to obtain stable latices with solids contents over 65% and viscosities of below 2500 mPa s−1 with little coagulum formation. The key parameter in determining latex stability, coagulum formation, and viscosity appears to be the the particle size distribution, and especially its modification attributed to secondary nucleation. Because it is not possible to eliminate water‐soluble monomers from the polymerization recipe, secondary (homogeneous) nucleation must be minimized by careful addition of the free‐radical initiator and choice of monomer feed flow rates. The nucleation of the third population in the trimodal latices is best accomplished with a mixed surfactant system because renucleation by anionic surfactant alone leads to detrimental changes in the particle size distribution (PSD) resulting from excessive flocculation of particles. In addition, it was found that the viscosity of the final products was not sensitive to small changes in the ionic strength of the latex, although neutralization to a pH of 6 effectively doubles the final latex viscosity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1916–1934, 2002; DOI 10.1002/app.10513

Study on controlling particle growth in seeded emulsion polymerization with regulated coagulation based on the electrostatic interactions

30wt% solid content, anionic seed copolymer latex P(methyl acrylate-co-methyl methacrylate) was prepared by conventional emulsion polymerization, and then the seeded emulsion polymerization was carried out accompanied with the electrostatic coagulation during the reaction in the presence of counter-ion species, such as cationic monomer and initiator. In this article, effects of cationic monomer (dimethyl aminoethyl methacrylate, DM) content, secondary monomer to seed polymer weight ratio, M/P and amount of emulsifier (polyoxyethylene nonylphenylether with 23 units of ethylene oxide, PEO23) were investigated on the effective particle growth and the stability of final latex. With 10wt% DM in monomer, M/P ratio at 2.0 were recommended. An optimal policy for handling the emulsifier content without the nucleation of secondary particles while achieving the controlled coagulative growth was proposed from the observations of polymer yield and particle size during the polymerization.

Study on the preparation and properties of styrene–butyl acrylate–silicone copolymer latices

Copolymer latices of styrene–butyl acrylate–silicone were prepared using a semicontinuous addition process and batch and monomer emulsion addition processes. The results showed that a stable latex with narrow particle size dispersion and a high monomer conversion can be obtained only by the semicontinuous addition process. The simultaneous free-radical and ionic copolymerization mechanisms were discussed. 3-Methacryloyloxypropyl trimethoxysilane in this work was used as a coupling agent to form a chemical bond between vinyl polymer and polysiloxane. It was found that the copolymerization reaction and the properties of latex and latex film were obviously influenced by silicone content. When the silicone content was less than 25 wt %, copolymerization proceeded readily and a stable latex could be prepared. With increasing silicone content, monomer conversion, latex stability, film hardness, and tensile strength decreased, whereas the water resistance and impact strength increased. Results of Soxhlet extraction, silicon analysis, and dynamic mechanical properties of latex polymer confirmed the occurrence of copolymerization. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3194–3200, 2001

Study on synthesis and morphology control of poly(4-vinylpyridine-co-butyl acrylate)/poly(styrene-co-butyl acrylate) composite microspheres

Monodispersed crosslinked cationic poly(4-vinylpyridine-co-butyl acrylate) [P(4VP-BA)] seed latexes were prepared by soapless emulsion polymerization, using 2,2′-azobismethyl(propionamidine)dihydrochloride (V50) as an initiator and divinylbenzene (DVB) or ethylene glycol dimethacrylate (EGDMA) as a crosslinker. The optimum condition to obtain monodispersed stable latex was investigated. It was found that the colloidal stability of the P4VP latex can be improved by adding an adequate amount of BA (BA/4VP = 1/4, w/w), and adopting a semicontinuous monomer feed mode. Subsequently, poly(4-vinylpyridine-co-butyl acrylate)/Poly(styrene-co-butyl acrylate) [P(4VP-BA)/P(ST-BA)] composite microspheres were synthesized by seeded polymerization, using the above latex as a seed and a mixture of ST and BA as the second-stage monomers. The effects of the type of crosslinker, the degree of crosslinking, and the initiators (AIBN and V50) on the morphology of final composite particles are discussed in detail. It was found that P(4VP-BA)/P(ST-BA) composite microspheres were always surrounded by a PST-rich shell when V50 was used as initiator, while sandwich-like or popcorn-like composite particles were produced when AIBN was employed. This is because the polarity of the polymer chains with AIBN fragments is lower than for the polymer with V50 fragments, hence leading to higher interfacial tension between the second-stage PST-rich polymer and the aqueous phase, and between PST-rich polymer and P4VP-rich seed polymer. As a result, the seed cannot be engulfed by the PST-rich polymer. Furthermore, the decrease of Tg of the second-stage polymer promoted phase separation between the seeds and the PST-rich polymer: sandwich-like particles formed more preferably than popcorn-like particles. It is important knowledge that various morphologies different from PST-rich core/P4VP-rich shell morphology, can be obtained only by changing the initiator, considering P4VP is much more hydrophilic than PST. The zeta potential of composite particles initiated by AIBN in seeded polymerization shifted from a positive to a negative charge. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1190–1203, 2002

Study on the preparation and properties of styrene–butyl acrylate–silicone copolymer latices

AbstractCopolymer latices of styrene–butyl acrylate–silicone were prepared using a semicontinuous addition process and batch and monomer emulsion addition processes. The results showed that a stable latex with narrow particle size dispersion and a high monomer conversion can be obtained only by the semicontinuous addition process. The simultaneous free‐radical and ionic copolymerization mechanisms were discussed. 3‐Methacryloyloxypropyl trimethoxysilane in this work was used as a coupling agent to form a chemical bond between vinyl polymer and polysiloxane. It was found that the copolymerization reaction and the properties of latex and latex film were obviously influenced by silicone content. When the silicone content was less than 25 wt %, copolymerization proceeded readily and a stable latex could be prepared. With increasing silicone content, monomer conversion, latex stability, film hardness, and tensile strength decreased, whereas the water resistance and impact strength increased. Results of Soxhlet extraction, silicon analysis, and dynamic mechanical properties of latex polymer confirmed the occurrence of copolymerization. © 2001 John Wiley &amp; Sons, Inc. J Appl Polym Sci 82: 3194–3200, 2001

Stabilization of Latex by Heterogemini Surfactants

Members of a new class of zwitterionic gemini surfactants have been evaluated as stabilizers of a polystyrene latex. The gemini surfactants, which previously have been found to adsorb strongly and form closely packed monolayers at hydrophobic surfaces, were found to be more efficient than the commonly used combination of anionic and nonionic surfactants in terms of providing heat and salt tolerance to the latex.

Surface morphology of asymmetric latex film prepared from blends of natural rubber and poly(methyl methacrylate) latexes

AbstractColloidally stable latex blends of natural rubber (NR) and poly(methyl methacrylate) (PMMA) latexes containing up to 50 wt.% PMMA can be prepared by mixing commercial NR ammoniated latex concentrate and monodisperse PMMA latex dispersion. The clarity and tackiness of the films obtained depend on the PMMA content; films become opaque and non‐tacky at &gt;30 wt.% PMMA content. The morphology of these films shows asymmetric distribution of the PMMA particles across the thickness of the film. There is preferential enrichment of PMMA particles at both the air/polymer and glass/polymer interfaces and a predominating NR interior. More PMMA particles are accumulated preferentially at the glass/polymer interface than at the air/polymer interface. The accumulation of the PMMA particles at the interface is strongly dependent on the size and concentration of the PMMA particles. The formation of these asymmetric latex films is explained in terms of the surface energetics, compatibility, Tg and density of the polymers, stability of the component latex, surface chemistry and particle size of the latex particles used. Copyright © 2001 John Wiley &amp; Sons, Ltd.

The preparation and spectral characterisation of vinylferrocene–styrene copolymer latexes

A series of vinylferrocene–styrene copolymer latexes having different vinylferrocene to styrene ratios were prepared via a free radical mechanism. Theoretical DLVO calculations have been used to model the aggregation behaviour of the polymer latexes with respect to a change in particle zeta potential. It has been shown that a critical value of the zeta potential of approximately −25 mV is necessary to confer latex stability. The Mössbauer spectra of the copolymers at 78 K showed the doublet characteristic of that expected for ferrocene and vinylferrocene monomer. The spectra also revealed that a second iron site was present. The Mössbauer parameters were consistent with oxidation having occurred yielding the ferrocenium ion. At room temperature, however, there was little evidence of the spectrum due to ferrocene. The major spectral feature had parameters similar to those for the ferrocenium site observed at the lower temperatures. The values obtained in this study are compared with those previously reported for other ferrocene-containing polymers, which were explained in terms of a cross-linked structure in the polymer consisting of two ferrocene units.

Study on ultrasonic induced encapsulating emulsion polymerization in the presence of nanoparticles

AbstractIn this paper, the ultrasonic induced encapsulating emulsion polymerization technique was used to prepare polymer/inorganic nanoparticle composites. The main affecting factors in ultrasonic induced encapsulating emulsion polymerization were studied systematically. The experimental results suggested that the pH value, the type of monomers, the type, content, and surface properties of nanoparticles, the type and concentration of surfactant have great influence on the ultrasonic induced encapsulating emulsion polymerization and the obtained latex stability. If selecting cationic emulsifier (such as cetyl trimethylammonium bromide), low water soluble monomer (such as n‐butyl acrylate and styrene), and hydrophobic nano silica, the inorganic nanoparticles could be encapsulated by polymers through ultrasonic irradiation successfully under alkalescent condition, forming a novel polymer/inorganic nanoparticles composite. The mechanism of ultrasonic induced encapsulating emulsion polymerization and the composite latex stabilization are proposed. © 2001 John Wiley &amp; Sons, Inc. J Appl Polym Sci 80: 1130–1139, 2001

Adsorption of polyelectrolytes on colloidal latex particles, electrostatic interactions and stability behaviour

Adsorption of polyelectrolytes on colloidal latex particles, electrostatic interactions and stability behaviour

Microemulsion polymerization of styrene stabilized by sodium dodecyl sulfate and diethylene glycol monoalkyl ether

The effects of the cosurfactants diethylene glycol monoalkyl ether [CiH2i+1O(CH2CH2O)jOH (CiEj; i=4, 6 and j=1, 2)] on the formation of an oil-in-water styrene (ST) microemulsion and the subsequent free radical polymerization were studied. For comparison, the data for the CiH2i+1OH (CiOH; i=4, 6) systems obtained from the literature were also included in this work. Sodium dodecyl sulfate was used as the surfactant. The pseudo three-component phase diagram (macroemulsion, microemulsion and lamellar gel phases) was constructed for each cosurfactant. The primary parameters selected for the polymerization study are the concentrations of cosurfactant and styrene. The number of latex particles nucleated is much smaller than that of the microemulsion droplets initially present in the reaction system. Limited flocculation of the latex particles occurs to some extent during polymerization. Among the cosurfactants investigated, the C4OH-containing polymerization system is the least stable. By contrast, the diethylene glycol monoalkyl ether group of CiEj tends to enhance the latex stability. CiEj is more effective in stabilizing the ST microemulsion and the subsequent polymerization in comparison with the CiOH counterpart.