Study On The Stability And Aggregation Behavior Of Surface Functionalized Polymer Colloidal Particles Under Stagnant Conditions

Colloid stability is the centerpiece of colloid science, and colloidal destabilization andaggregation phenomena are widely involved in many natural and industrial processes.Understanding the colloidal stability, aggregation, the aggregation kinetics and the structure ofthe resulting of aggregates has great importance not only for fundamental researches, but alsofor their applications. Industrial polymer colloids and bovine serum albumin (BSA) have beenchosen for the studies, all kinds of lighting scattering techniques have been used to monitorand characterize their stability and aggregation behavior, aiming to quantify the contributionof each functional group to colloidal particle stability and its influence on particle aggregationand coalescence behavior, rich the theories of colloid science, and provide supervision for theapplication of polymers in industry and daily life.Dynamic light scattering (DLS) and static light scattering (SLS) have been introduced tocharacterize Fuchs stability ratio W for six polymer latices of different type, differentconcentration functional groups, different electrolyte types and concentration at different pHvalues to quantify the contribution of each functional group to polymer stability. Results showthat the particle stabilized purely by sulfate groups (-SO₄) on the surface has the loweststability. The introduction of both acrylic acid (AA) and acrylamide (AM) increases particlestability. For the AM case, when pH<3, the colloidal stability is higher for1%AM than for2%AM due to the effect of NH₂protonation, leading to positive charges which partlyneutralize the negative charges and thus decreases the net charges, however, for pH>3, suchprotonation is negligible, and the stability is higher with2%AM. For the AA case, both atvery low (pH₃) and very high pH values (pH≈8), the stability is rather similar between1%and2%AA, but in the intermediate pH (pH≈5), it is higher with2%AA, indicating upperlimit of the AA contribution to particle stability. The stability of polymer latices modified byboth AA and AM is pH responsive. The best stable latex among all the six cases is the onewith both1%AA and1%AM.After introduction of AA, there generates polyelectrolyte brushes on the surface of thepolymer particles, and the stability increases with increasing pH, however, there exists upperlimit at pH8for the particle with2%AA and the stability is very close to pH5. A generalizedstability model has been introduced to make simulation of Fuchs stability ratio W and pHvalues to confirm pH responsive stability and LEA phenomenon. Results show that theassociation constant of H+with-COO is7.610⁶L/mol which is much higher than the value for monolayer macromolecule PAA, i.e.6.3104L/mol, which is reasonable and thereason is because of the protonation of PAA brushes, part of them is buried inside at low pH,does not take part in the association equilibria. Furthermore, the association constant of Na+with-COO is7.00for the case of2%AA, higher than the value (i.e.2.30) for the case of1%AA, confirming that the inner part of the brush protonated more than the outer part, i.e. morethan surface monolayers of macromolecular chains, on the other hand, it confirms the LEAphenomenon.The fractal dimension (Df) of the clusters formed during the aggregation of colloidalsystems reflects correctly the coalescence extent among the particles. In this work we proposeto use the fast small-angle light scattering (SALS) technique to determine the Dfvalue duringthe aggregation. It is found that in the diffusion-limited aggregation (DLCA) regime, the Dfvalue can be correctly determined from both the power-law regime of the average structurefactor of the clusters and the scaling of the zero angle intensity versus the average radius ofgyration. The obtained Dfvalue is around1.75which is between1.75and1.85typical ofDLCA regime for rigid particle. In the reaction-limited aggregation (RLCA) regime, due tocontamination of small clusters and primary particles, the power-law regime of the averagestructure factor cannot be properly defined for the Dfestimation. However, the scaling of thezero angle intensity versus the average radius of gyration is still well-defined, thus allowingone to estimate the Dfvalue, i.e., the coalescence extent. The value of Dfunder RLCAcondition is between2.20².70, which is different from the typical value for rigid particleaggregation. i.e. in the range between2.00and2.10, and the value of Dffor coalescencedaggregates is between2.10³.00(3.00for fully coalescence case), which means partialcoalescence occurred for the current colloid system under RLCA regime. This is the first timeto find that coalescence is related to aggregation regime.We study, using wide-angle and small-angle light scattering techniques, stability andaggregation/gelation behaviors of denatured filamentous bovine serum albumin preaggregates(BSA-PAs), induced by CaCl₂. It is observed that transparent filamentous gels can be formednot only at low CaCl₂concentrations but also at high CaCl₂concentrations, while the turbidgels are obtained at intermediate CaCl₂concentrations. Although the filamentous gels at lowCaCl₂concentrations and turbid gels at intermediate CaCl₂concentrations are consistent withthe literature observations, the filamentous gels at high CaCl₂concentrations have to beexplained by different mechanisms. The latter is attributed to the repulsive hydrationinteractions originating from increased surface dipoles generated by counterion binding. Since such surface dipole-induced hydration is very short-range and occurs mainly on charged orpolar patches of proteins (thus protected from aggregation), aggregation of the filamentousBSA-PAs at hydrophobic patches at the two ends is still possible, leading to the formation offilamentous gels.In order to improve the mechanical and chemical properties, especially the solventresistance of the cast films formed from normal waterborne polyurethane (PU) dispersions, anovel ultraviolet (UV)-curable epoxy and acrylate-modified waterborne polyurethanedispersion (UV-EP-AC-WPUD) and its film with high crosslink density and excellent filmproperties were prepared and studied in this paper.4%epoxy resin E-20was introduced in PUchain by grafting reaction between epoxy resin and polyurethane prepolymer terminated withthe-N=C=O group. The C=C bond was introduced in PU chain by the chain-extendingreaction of-NCO in polyurethane prepolymer with two hydroxyl vinyl monomers PEDA andsingle-hydroxyl vinyl monomers PETA, and the obtained maximum C=C content was up to4.65meq/g.3%photoinitiator Irgacure2959was used to initiate the polymerization of C=Cbond in cast films, and the gel content of the UV-EP-AC-WPUD films could reach up to91%after12.0s UV-radiation, which meant the rate of the polymerization and the crosslinking rateof C＝C bond was high, and the obtained UV-EP-AC-WPUD film was highly-crosslinkedand insoluble in solvent. The water absorption, solvent resistance, gel content, pendulumhardness and tensile strength of the cured film were studied, and Fourier transform infraredspectroscopy (FTIR) analysis and film study results showed that the UV-cured EP-WPUDfilms including epoxy resins and hydroxyl-containing vinyl monomers had excellentmechanical and chemical properties; Thermo gravimetric analysis (TGA) also indicated thatthermal stability of the film was improved significantly.