Triblock copolymer measurements

Brown, W Schillen, K Hvidt, S, Triblock Copolymers in Aqueous Solution Studied by Static and Dynamic Light Scattering and Oscillatory Shear Measurements. Influence of Relative Block Sizes, Journal of Physical Chemistry 96, 038, 1992. 

The use of lightly crosslinked polymers did result in hydrophilic surfaces (contact angle 50°, c-PI, 0.2 M PhTD). However, the surfaces displayed severe cracking after 5 days. Although qualitatively they appeared to remain hydrophilic, reliable contact angle measurements on these surfaces were impossible. Also, the use of a styrene-butadiene-styrene triblock copolymer thermoplastic elastomer did not show improved permanence of the hydrophilicity over other polydienes treated with PhTD. The block copolymer film was cast from toluene, and transmission electron microscopy showed that the continuous phase was the polybutadiene portion of the copolymer. Both polystyrene and polybutadiene domains are present at the surface. This would probably limit the maximum hydrophilicity obtainable since the RTD reagents are not expected to modify the polystyrene domains. 

The absolute number of monomer units of the polystyrene (m) and polybutadiene (n) blocks were determined by combined H-NMR and GPC measurements. The triblock copolymer is a commercially available polystyrene-b-polybutadiene-i-polystyrene polymer and was purchased from Aldrich (M = 100,000 28 wt% polystyrene). 

Recent studies on PEO-PPO, PEO-PBO di- and triblock copolymers include the works of Bahadur et al. [121], who examined the role of various additives on the micellization behavior, of Guo et al. [122], who used FT-Raman spectroscopy to study the hydration and conformation as a function of temperature, of Booth and coworkers [ 123], who were mainly interested in PEO-PBO block copolymers with long PEO sequences, and of Hamley et al., who used in situ AFM measurements in water to characterize the morphology of PEO-PPO micelles [56,57]. 

The Tg values of all investigated triblock copolymers are plotted in Eig. 20. The increasing trend in the measured values is due to the incorporation of monomers with rigid substituent such as methyl or phenyl. Moreover, the Tg values did not... 

Fig. 16 Representative data from the surface wrinkling metrology, demonstrating the unprecedented range of moduli and the precision that the methodology unlocks a modulus of a thickness gradient library of PS (reproduced with permission from [72]) b modulus as a function of composition for P(S-I-S) triblock copolymer blends c modulus as a function of thickness for ultrathin PS films (reproduced with permission from [74]). The lines are meant to guide the eye and the error bars represent one standard deviation of the data, which is taken as the experimental uncertainty of the measurement...

Rheological measurements also show that PS-PI diblock and PS-P1-PS triblock copolymers with /< 0.2 (for either block) exhibit a liquid-like viscoelastic response, even at temperatures below the ODT (Adams et al. 1994 Han et al. 1995 Sakamoto et al. 1997). Han et al. (1995) and Sakamoto et al. (1997) have observed that the ODT cannot be located for these samples based on a discontinuity in the isochronal shear moduli as a function of temperature but can be obtained from plots of logG versus logG" (Fig. 2.4(c)). 

Takahashi et al.67) prepared ionene-tetrahydrofuran-ionene (ITI) triblock copolymers and investigated their surface activities. Surface tension-concentration curves for salt-free aqueous solutions of ITI showed that the critical micelle concentration (CMC) decreased with increasing mole fraction of tetrahydrofuran units in the copolymer. This behavior is due to an increase in hydrophobicity. The adsorbance and the thickness of the adsorbed layer for various ITI at the air-water interface were measured by ellipsometry. The adsorbance was also estimated from the Gibbs adsorption equation extended to aqueous polyelectrolyte solutions. The measured and calculated adsorbances were of the same order of magnitude. The thickness of the adsorbed layer was almost equal to the contour length of the ionene blocks. The intramolecular electrostatic repulsion between charged groups in the ionene blocks is probably responsible for the full extension of the... 

Kawaguchi et al.125) prepared an ionene-oxyethylene-ionene (IEI) triblock copolymer with the molecular weight 72 X 103 and measured its surface tension in aqueous KBr. They also determined by ellipsometry the adsorbance and the thickness of the adsorbed polyelectrolyte layer at the air-KBr solution interface as a function of the KBr concentration. The data obtained indicate that this copolymer is surface-active and that the effect of added KBr on the surface tension is stronger than in the case of polyoxyethylene (POE). 

Microscopic foam films from amphiphilic ABA triblock copolymers have been used to assess steric interactions. Most of the work on copolymers [128,129] has been carried out with the Thin Liquid Film-Pressure Balance Technique (see Chapter 2, Section 2.1.8). Nevertheless, some intriguing results have been obtained with the dynamic method for surface force measurement [127]. 

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