The binding of dodecyltrimethylammonium bromide (DoTab) to poly(acrylic acid) (PAA) at different degrees
of neutralization (α) was investigated using isothermal titration calorimetry (ITC) and laser light scattering
(LLS) techniques. The surfactant binds to the polymer at all α; however, the mechanism varies. When α is
lower than a critical value (αC), the hydrocarbon chains of DoTab cooperatively bind to the apolar segments
of PAA driven by hydrophobic interaction at very low DoTab concentration (C
DoTab ≤ 0.2 mM). In this
binding region, the ITC profile exhibits a significant exothermic peak and the mixture precipitates, which is
attributed to the interchain complexation via hydrogen bonding induced by the binding. The precipitation is
soon resolubilized with further addition of surfactant as more DoTab micelles are bound to the polymer
backbones with their ionic headgroups extending outward. When α > αC, the hydrophobic binding ceases as
the polymer is progressively ionized and DoTab binds to the charged polymer chains driven by electrostatic
attraction. The condensed counterions on the charged polymer chains are released via the ion-exchange process,
resulting in an endothermic maximum on the ITC profile. The value of αC determined from ITC is
approximately 0.3, which is reasonably close to the theoretical value derived from the Manning's counterion
condensation theory (approximately 0.35).
Abstract-Atom transfer radical polymerisation (ATRP) technique was used to synthesize poly(methacrylic acidblock-methyl methacrylate) (P(MAA 102 -b-MMA 10 )) copolymer in order to study the aggregation behavior in aqueous solution over the course of neutralization. A combination of static and dynamic light scattering (SLS, DLS) and potentiometric titration techniques were used to investigate the size and shape of the micelle at various degrees of neutralization. The hydrodynamic radius (R h ) determined from dynamic light scattering increases from ∼26nm (for unneutralized) to ∼42nm (for completely neutralized sample). Both potentiometric and laser light scattering studies indicate the formation of a core shell micelle. The weighted average molecular weights of the polymer and micelle are 1.18x10 4 and 2.25 x 10 5 g/mol respectively, which suggests that the aggregation number of the micelle is ~20.
Potentiometric titration, static and dynamic light scattering, and isothermal titration calorimetry were used to
study the salt effects on the dissolution behavior of Hydrophobically Modified Alkali-Soluble Emulsion (HASE)
polymer emulsions in aqueous medium.The negative logarithm dissociation constant (pK
a) curves reveal that
HASE polymer exhibits a conformational transition from a compact hard sphere to a random coil during the
process of neutralization. Addition of a neutral salt reduces the energy necessary to extract protons from
carboxylic acid groups, which favors the neutralization process. The latex particles expand with extent of
neutralization (α) in the early stage of titration, thereafter the swollen particles dissociate into smaller clusters.
The addition of salt screens the electrostatic repulsion between the polymer chains, and consequently reduces
the hydrodynamic radius (R
h) of the polymer clusters. The results also show that the polymer chains tend to
form intramolecular association rather than intermolecular association in the presence of salt, which promotes
the dissociation of polymer particles. The thermodynamic quantification of the dissolution behavior of model
HASE polymer was achieved using the isothermal titration calorimetric technique. The results reveal that
neutralization is an exothermic process dominated by enthalpy. The comparison of the titration data in different
salt conditions show that the ΔG for the neutralization process is more negative at high salt content, suggesting
that the dissolution is enhanced by the presence of a neutral salt.
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