Eric Scott Johnson

Surface Deposition and Phase Behavior of Oppositely Charged Polyion/Surfactant Ion Complexes. 1. Cationic Guar versus Cationic Hydroxyethylcellulose in Mixtures with Anionic Surfactants

Mixtures of cationic guar (cat-guar) or cationic hydroxyethylcellulose (cat-HEC) with the anionic surfactants sodium dodecyl sulfate or sodium lauryl ether-3 sulfate have been investigated by a wide range of complementary techniques (phase studies, turbidity measurements, dynamic light scattering, gel-swelling experiments, and in situ null ellipsometry), with the following objectives in mind: (1) to establish the relationship between the bulk phase behavior (precipitation and redissolution) of the polyion/surfactant ion complexes and formation/deposition of such complexes at silica surfaces and (2) to obtain molecular interpretations of the large, previously unresolved, quantitative differences between the various investigated mixtures. There were clear similarities, for each studied system, between the bulk phase behavior, gel swelling, and surface deposition on increasing surfactant concentration. This is because all phenomena reflect the polyion/surfactant ion binding isotherm: an initial binding step at a low critical association concentration (cac) of the surfactant and a second more-or-less cooperative binding step beginning at a second cac, the cac(2). The details of the interactions are system-specific, however, and cat-guar/surfactant mixtures generally had larger precipitation regions and gave rise to larger adsorbed amounts on silica compared to mixtures with cat-HEC of a similar charge density. The observed quantitative differences are attributed to a difference in the hydrophobicity of the polyions. For cat-guar, the comparatively weak hydrophobic polyion/surfactant attraction is seen as a very gradual binding commencing at the cac(2) and continuing past the bulk critical micelle concentration of the surfactant, resulting in an unusually large phase-separation region. For cat-HEC, the dissolution of the precipitate takes place at lower surfactant concentrations because of a stronger hydrophobic interaction between the surfactant and the polyion. The results have implications for the successful design of oppositely charged polyelectrolyte/surfactant formulations for surface deposition applications.

Surface Deposition and Phase Behavior of Oppositely Charged Polyion-Surfactant Ion Complexes. Delivery of Silicone Oil Emulsions to Hydrophobic and Hydrophilic Surfaces.

The adsorption from mixed polyelectrolyte–surfactant solutions at hydrophobized silica surfaces was investigated by in situ null-ellipsometry, and compared to similar measurements for hydrophilic silica surfaces. Three synthetic cationic copolymers of varying hydrophobicity and one cationic hydroxyethyl cellulose were compared in mixtures with the anionic surfactant sodium dodecylsulfate (SDS) in the absence or presence of a dilute silicone oil emulsion. The adsorption behavior was mapped while stepwise increasing the concentration of SDS to a polyelectrolyte solution of constant concentration. The effect on the deposition of dilution of the bulk solution in contact with the surface was also investigated by gradual replacement of the bulk solution with 1 mM aqueous NaCl. An adsorbed layer remained after complete exchange of the polyelectrolyte/surfactant solution for aqueous NaCl. In most cases, there was a codeposition of silicone oil droplets, if such droplets were present in the formulation before dilution. The overall features of the deposition were similar at hydrophobic and hydrophilic surfaces, but there were also notable differences. SDS molecules adsorbed selectively at the hydrophobized silica surface, but not at the hydrophilic silica, which influenced the coadsorption of the cationic polymers. The largest amount of deposited material after dilution was found for hydrophilic silica and for the least-hydrophobic cationic polymers. For the least-hydrophobic polyions, no significant codeposition of silicone oil was detected at hydrophobized silica after dilution if the initial SDS concentration was high.

Molecular Orientation and Stacking of Perylenetetracarboxylic Diimide Derivatives in Langmuir-Blodgett Monolayers: Part I

The molecular organization in Langmuir-Blodgett (LB) monolayers for five organic dyes with a common chromophore moiety was studied. With the use of transmission and reflection-absorption (FT)IR spectroscopy (RAIRS), the orientation of the chromophore units in the LB monolayer was determined. The results obtained with carbonyl and C=C stretching vibrations exclude a flat-on orientation of the chromophore moiety and may be rationalized in terms of a tilted head-on organization of the chromophore on the Ag, ZnS, and Ge surfaces. The tilt angle, φ, formed between the direction of the dynamic dipole moment and the normal to the surface of the film was determined from the combined infrared data obtained in a transmission geometry and in RAIRS. The aromatic-aromatic interaction plays a significant role in determining the molecular alignment in the Langmuir and LB monolayers.

Colloidal Structure and Physical Properties of Gel Networks Containing Anionic Surfactant and Fatty Alcohol Mixture

We investigated the mechanical properties, thermal behavior, physical state, and colloidal structure of a model gel network formulated with various ratios of sodium dodecyl sulfate polyacrylamide (SDS) and cetyl/stearyl fatty alcohol (FA) mixture in constant amounts of water (89%). The metastable gel, formed by slowly cooling stirred samples from temperatures above the chain melting temperature (Tm) of the long chain FA, has a lamellar structure with a periodic inter bilayer spacing of approximately 30 nm. The bilayers remain homogeneous with SDS being immobilized in the FA matrix upon chain freezing. The chain length mismatch leads to an increased structural disorder among the alkyl chains upon SDS incorporation among the FA. As a result, the elastic modulus decreased with increasing SDS content. Conclusions were based on a large number of experiments involving differential scanning calorimetry, rheology, 1H NMR spectroscopy, and small angle x-ray scattering. Results from this work have uncovered the physical nature of these networks and gave insight into the role of anionic surfactants on the assembly, physical state, and mechanical properties of gel networks.

Surface-enhanced fluorescence of aggregates in Langmuir-Blodgett monolayers

The geometry of the molecular organization in monolayers seems to be a key factor in the formation of aggregates. In the present work, monolayers of perylene tetracarboxylic derivatives have been fabricated under conditions leading to different molecular orientations in the film. Monolayers of the neat dye material, and mixed monolayers, were prepared at different pH values of the subphase and transferred to glass slides at constant pressure. Monolayers were also transferred to glass substrates at various points in the surface pressure-area isotherm. Steady state surface-enhanced fluorescence measurements were used to characterize the aggregate formation. Surface-enhanced resonant Raman scattering (SERRS) was observed and used as an internal reference in the fluorescence measurements.

Book Reviews: Handbook of Chemometrics and Qualimetrics, Understanding Mass Spectra: A Basic Approach, High Resolution Spectroscopy

Handbook of Chemometrics and Qualimetrics, Part B. B. G. M. Vandeginste, D. L. Massart, L. M. V. Buydens, S. De Jong, P. L. Lewi, and J. Smeyers-Verbeke . Elsevier, Amsterdam , 1998. Pp. 713. Price

Shampoo containing a gel network

201, ISBN 0-444-8285 3-2. This book is presented as 17 chapters, numbered 28±44 to be consistent with part A. Part A deals with experim ental design and testing, part B with analysis and presentation of results. After an introductor y chapter, the book leads off with a substantial discussion of vectors and matrices. This material, an expansion of Chapter 9, is essential to understandi ng of many of the topics that are covered in subsequent chapters. As an example, the discussion of row and column spaces provides background for discussions of principal component s analysis in Chapter 31, for curve resolution in Chapter 34, and for principal components regression in Chapters 35 and 36. The book has been carefully written. Logical gaps in explanations have been avoided, and the discussion is couched in terms that make it accessible to chemists. The chapter heads are as follows: 30, cluster analysis; 31, analysis of measurem ent tables; 32, analysis of contingency tables; 33, supervised pattern recognition ; 34, curve and mixture resolution; 35, relationship s between measurem ent tables; 36, multivariate calibration; 37, qualitative structure-ac tivity relationship s; 38, analysis of sensor y data; 39, pharmacokinetic models; 40, signal processing; 41, Kalman ® ltering; 42, operations research; 43, arti® cial intelligence; and 44, arti® cial neural networks. Literature references are provided with each chapter. Very often there are additional items of recommended additional reading. The ® rst seven of these complete a major theme of the two volumes, qualitative and quantitative methods for complex data sets. The emphasis is on visualization of features of complex sets in Chapters 30 ±33. Chapter 34 presents application s of factor analysis for curve resolution. In Chapter 35, a more quantitative approach is taken. In Chapter 36 the formal methods of quantitative analysisÐ classical least-squares, inverse least-squares, principal components regression, and partial least-square sÐ are compared. In Chapter 37, aimed at the pharmaceutical industr y, the application of the full range of chemometrics techniques to structureactivity relationship s in drug design is discussed. Chapter 38 is concerned with systematic handling of sensor y data in applications such as product formulation in the food industr y. Chapter 39 deals with kinetic modeling for drug deliver y. The major emphasis is on singleand two-compartment models of effective drug concentratio ns. With Chapters 40 and 41, the direction again changes to a discussion of signal processing. In Chapter 40 the emphasis is on the Fourier transform . The chapter ends with brief discussions of the Hadamard and wavelet transform s. In Chapter 41, recursive regression, the Kalman ® lter, and the adaptive Kalman ® lter are discussed. Chapter 42 presents an introductio n to operations research. This discussion consists of a set of techniques that can be used for optimization of operations such as allocation, inventory, replacem ent, queuing, and routing. Expertand knowledge -based arti® cial intelligence system s are described in Chapter 43. These systems are described in terms of three components: the knowledge base, the inference engine, and the interaction module. Examples are used to clarify the operation of each component type. The book closes with a ® fty-page discussion of neural networks. The emphasis is on multilayer feed-for ward system s with sigmoidal transfer functions, one hidden layer using back-propag ation learning. Several references are given to speci® c chemical applications.