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Intrapolymer self-association of random copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) and N-dodecylmethacrylamide (DodMAm) with varying compositions in aqueous solution was investigated by various fluorescence techniques. The polymers were labeled with 1 mol % of naphthalene (Np) or pyrene (Py) or doubly labeled with Np (4 mol %) and Py (1 mol %). Vibronic fine structures of Py fluorescence, lifetimes of Np and Py fluorescence, intrapolymer nonradiative energy transfer (NRET) from singlet excited Np to ground-state Py labels, and fluorescence quenching by thallium cations were investigated as a function of the DodMAm content (f Dod) in the copolymers with or without added salt. Results from all these fluorescence studies indicate that with increasing f Dod, hydrophobic association commences at f Dod ≅ 20 mol % in pure water and at f Dod ≅ 10 mol % in 0.1 M NaCl, showing a saturation tendency near f Dod ≅ 40 mol % in the salt solution. In contrast, viscosity data show that the polymer size markedly decreases in the regime 5 < f Dod < 20 mol % owing to intrapolymer hydrophobic association of dodecyl groups. This decrease in the macroscopic size of the polymer in the low f Dod regime could not be detected by any fluorescence techniques employed. Although the viscosity data do not show any further contraction of the polymer chains at f Dod > 20 mol %, the NRET results indicate a considerable increase in the compactness of polymer chains at f Dod > 20 mol %. The combination of these fluorescence techniques proved to provide a sensitive tool to detect hydrophobic associations and conformational changes in the hydrophobically modified polymers, while viscosity reflects only global changes in the polymer size.

The interaction between pyrene-labeled poly(acrylamido)-2-methylpropane sulfonate) (PyPAMPS) and mixed micelles of n-dodecylhexaoxyethylene glycol monoether/n-hexadecyltrimethylammonium chloride (C12E6/CTAC) was studied by turbidimetry, quasielastic light scattering (QELS), fluorescence quenching, and UV spectroscopy. The present report focuses on the effect of the pyrene label on the polymer-micelle interaction. With nonlabeled PAMPS, we observe by turbidity and QELS a critical mole fraction of ionic surfactant (Yc) corresponding to the onset of polyelectrolyte-micelle interaction. The same Yc is observed by turbidity and QELS for PyPAMPS. However, PyPAMPS shows a lower additional transition by the same methods, which we refer to as "Yc1" to distinguish it from "Yc2" which is seen for both PAMPS and PyPAMPS. Steady-state fluorescence, in the presence of a hydrophobic quencher (N,N-dimethylaniline) solubilized in the micelles, also shows a discontinuity at Yc1. Therefore, we conclude that Yc1 and Yc2 correspond to the binding of micelles to polymeric pyrene sites and AMPS sites, respectively. Analysis of UV spectra at varying Y demonstrates that the polymer-bound pyrene penetrates inside micelles and resides at or near the hydrophobic core. These results indicate preferential binding of micelles to pyrene binding sites; nevertheless, both Yc1 and Yc2 show a linear dependence on the square root of the ionic strength. This dependence suggests the dominant role of electrostatic forces, consistent with the observation that nonionic micelles will not bind to PyPAMPS. We conclude that conjoint hydrophobic and electrostatic effects determine the interaction between PyPAMPS and C12E6/ CTAC mixed micelles.

The interaction between poly(sodium 2-(acrylamido)-2-methylpropanesulfonate) labeled with 1 mol % pyrene (PyPAMPS) and mixed micelles of hexaethylene glycol n-dodecyl monoether (C12E6) and n-hexadecyltrimethylammonium chloride (CTAC), in which N,N-dimethylaniline (DMA) was solubilized, was studied by steady-state and time-dependent fluorescence quenching by varying the mole fraction of CTAC (Y) in the mixed micelle. At Y < 0.05, fluorescence quenching is essentially dynamic, arising from collisional encounters of the pyrene sites and DMA-carrying mixed micelles. Strong quenching begins to occur at Y ≅ 0.05, corresponding to the onset of polyelectrolyte−micelle interactions. In the region 0.05 < Y < 0.09, the quenching was shown to occur via transient complex formation between PyPAMPS and the mixed micelle. Changes in the vibrational structures of fluorescence spectra of pyrene in PyPAMPS indicate that pyrene groups are inserted in the hexa(oxyethylene) phase of the mixed micelle when the polymer−micelle complex is formed. The extent of quenching reaches a limiting value at Y > 0.11 in excess micelle solution, corresponding to the state in which all pyrene groups are micelle-bound.

Fluorescently labeled amphiphilic polyelectrolytes have been prepared by free-radical copolymerization in dimethylformamide using azobis(isobutyronitrile) as the initiator of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS) and (1) N- [4-(1-pyrenyl)butyl]-N-n-octadecylacrylamide (PyODA) in 98:2 and 95:5 molar ratios, (2) N- [2-(1-naphthyl)ethyl]-N-n-octadecylacrylamide (NpODA) in 98:2 and 95:5 molar ratios, and (3) a mixture of the two labeled monomers in a molar ratio of 95:4:1 (AMPS: NpODA:PyODA). The solution properties of the copolymers in water and in salt solutions have been studied by viscometry, 1 H NMR spectroscopy, and fluorescence spectroscopy. Evidence from nonradiative energy transfer between excited naphthalene (Np*) and pyrene (Py) in aqueous solutions of the doubly labeled polymers points to the formation of polymeric micelles. The inefficiency of nonradiative energy transfer between Np* and Py in mixed solutions of the singly labeled polymers indicates that the micelles are mostly unimolecular. The quenching of fluorescence of polymer-linked pyrene by nitromethane and thallium nitrate has been used to assess the accessibility of the chromophore to neutral molecules and to cationic species, respectively, in water and in solutions of increasing ionic strength. The results are discussed in light of previous studies of the properties in solution of neutral polymers carrying the same hydrophobic substituents as PAMPS-Py(Np)ODA and of amphiphilic PAMPS substituted with various other hydrophobic groups.

Interactions of random copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate and N-dodecylmethacrylamide (DodMAm) with n-dodecyl hexaethylene glycol monoether (C12E6) with and without added n-hexadecyltrimethylammonium chloride (CTAC) in 0.2 M NaCl aqueous solutions were investigated by fluorescence and light-scattering techniques. The polymers with the DodMAm contents (f Dod) ranging from 10 to 50 mol % were singly labeled with pyrene (1 mol %) or doubly labeled with pyrene (1 mol %) and naphthalene (4 mol %). These polymers form unimolecular micelles (unimer micelles) owing to intramolecular self-association of polymer-bound dodecyl groups, the compactness of the unimer micelle depending on f Dod. The unimer micelles of the polymers with f Dod ≥ 30 mol % have a particularly compact nanostructure where polymer chains are highly collapsed. In the presence of C12E6/CTAC mixed micelles, the polymer with f Dod = 10 mol % abruptly undergoes bulk phase separation as the mole fraction of CTAC (Y) in the mixed micelle is increased to a certain critical level (Y p) (i.e., Y p ≈ 0.15). With an increase in f Dod, the bulk phase separation becomes significantly less abrupt, accompanying a marked increase in Y p. For the polymers with f Dod ≥ 40 mol %, no such bulk phase separation was observed in a region of 0 ≤ Y ≤ 0.6. Intrapolymer nonradiative energy transfer indicates that the unimer micelles of the polymers with f Dod ≥ 30 mol % are unfolded by interactions with C12E6. The formation of soluble polymer−micelle complexes was manifested by an increase in the hydrodynamic radius (R h) upon addition of C12E6 to polymer solutions. The R h for the unimer micelle with f Dod = 50 mol % increased from 8.2 to 15.8 nm by the addition of 5.0 mM of C12E6 at a polymer concentration of 1.5 g/L. The R h at Y = 0 further increased to 21.5 nm as CTAC was added to Y = 0.07, indicating an interplay of hydrophobic and electrostatic interactions in the complexation between the unimer micelle and C12E6/CTAC mixed micelles.

No abstract

Liquid crystal displays are now indispensable in everyday life. The display characteristics considerably depend on the configuration of liquid crystal (LC) molecules and interactions between the LC molecules and an alignment film surface. In this paper, we introduce various methods to control parameters that dominate the LC alignment. These parameters include order parameters, the pretilt angle, the director direction, and surface anchoring strength. We also introduce their evaluation methods. In particular, recent alignment film‐free technology is explained in detail. In addition, details of how these parameters are related to the display characteristics, particularly wide viewing angles and fast response characteristics, are described primarily with reference to recent technologies.