The objective of the study was to examine the changes in central nervous system (CNS) activity and physical behaviour during induction and awakening from CO2 anaesthesia. Two studies, each using pigs immersed into 90% CO2 gas for a period of 60s were performed. In study 1, we monitored middle latency auditory evoked potentials (changes in latencies, amplitudes and a depth of anaesthesia index), electroencephalographic parameters (delta, theta, alpha and beta electroencephalographic power and 95% spectral edge frequency) and heart rate; and in study 2, we monitored body movements and arterial and venous partial pressure of CO2 and O-2. No behavioural signs of distress were observed during the early part of the induction. The swine exhibited muscular activity from 13-30s after induction-start as well as during awakening from anaesthesia, possibly because of a transitory weaker suppression of the brain stem than of the cortex. The CNS and blood gas parameters started to change from the very start of induction. The CNS suppression lasted only approximately one minute after the end of the induction period. The two studies indicated a good temporal relationship between changes in amplitude, depth of anaesthesia index, spectral edge frequency, and arterial P-CO2 during the induction period.

A method is described for measuring middle-latency auditory evoked potentials (MLAEP) in consciously awake, non-sedated pigs during the induction of thiopentone anaesthesia (0.6 ml/kg, 2.5% thiopentone solution). It was done by using autoregressive modelling with an exogenous input (ARX). The ability to perceive pain during the induction was compared with (1) the changes in latencies and amplitudes of the MLAEP, (2) the change in a depth of anaesthesia index based on the ARX-model and (3) the change in the 95% spectral edge frequency. The pre-induction MLAEP was easily recordable and looked much like the one in man, dogs and rats. The temporal resolution in the ARX method was sufficiently high to describe the fast changes occurring during induction of thiopentone anaesthesia. As previously reported from studies in man, dogs and rats, induction of thiopentone anaesthesia resulted in significantly increased latencies and decreased amplitudes of the MLAEP trace as well as in a significantly reduced depth of anaesthesia index and spectral edge frequency. None of the changes, however, related well to the ability to react to a painful stimulus. Whether an ARX-based depth of anaesthesia index designed especially for pigs might be better than the present index (designed for man) for assessing depth of anaesthesia must await the results of further studies.

Static and dynamic light scattering were used to study changes in the internal polymer segment density and particle swelling during the alkalization of aqueous dispersions of internally cross-linked, acid-containing latices (microgels). Upon neutralization, the microgels swell in excess of 200 times by volume, as evidenced by the measured hydrodynamic radius, R(h). Pronounced negative deviations of the ratio of the radius of gyration, R(g), to R(h) from the known value for homogeneous spheres along with curvature in Guinier plots of the angular dependent light scattering intensity indicate a nonuniform polymer segment density distribution within the microgels. Utilizing a simplistic core-shell model, we have determined the influence of the degree of neutralization, microgel cross-link density, and ionic strength on the nonuniform microgel swelling.

The polymerization of styrene in three-component oil-in-water microemulsions made with the cationic surfactant dodecyltrimethylammonium bromide is studied by dilatometry and quasielastic light scattering as a function of type and concentration of initiator. Fast polymerization rates, high conversions, and high molecular weight polymers are achieved with both oil-soluble (AIBN) and water-soluble (potassium persulfate) initiators. The rate of polymerization shows initiation and termination intervals, but no constant-rate interval is observed. Stable monodisperse microlatexes are obtained with both types of initiators. For both AIBN and potassium persulfate, polystyrene molecular weight is proportional to initiator concentration [I]−0.4 and particle radii decrease as [I]−0.2. Polymerization initiation occurs in or at the microemulsion droplets, and polymer particles grow by recruiting monomer and surfactant from uninitiated swollen micelles.

When subjected to low stresses, an abrupt cessation of flow (solidification) is observed in concentrated dispersions of hard sphere-like colloidal particles. This is due to the formation of colloidal crystals, as evidenced by opalescence when illuminated by white light. The elastic polycrystalline structure is stable if unperturbed but can be destroyed by exceeding a yield stress.

The shear viscosity of monodisperse and binary mixtures of internally-cross-linked polystyrene latices (microgels) dispersed in bromoform has been studied as a function of the applied shear stress, total microgel concentration, and concentration ratio of large to small microgels. For highly cross-linked monodisperse microgels with hydrodynamic radii of 84 and 141 nm, the limiting viscosities at both zero and infinite shear rates, eta0 and eta(infinity), are independent of particle size and exhibit the same scaling with volume fraction as hard-sphere-like dispersions. Also in agreement with experimental data for hard-sphere-like dispersions, the critical stress, defined as the stress at which eta = (eta0 + eta(infinity))/2, displays a maximum as a function of the microgel volume fraction. For binary mixtures having a constant microgel volume fraction, the viscosity exhibits a minimum as a function of the fraction of small particles, reflecting the more efficient packing due to polydispersity. A semiempirical model of the viscosity of microgel mixtures, based on the scaling of the viscosity with "excluded volume", is proposed. The excluded volume parameter is defined in terms of the hard-sphere osmotic compressibility for mixtures.

The effect of particle size, total particle volume fraction, and volume ratio of large to small particles on the equilibrium structure of concentrated mono- and bidisperse mixtures of highly cross-linked polystyrene latex particles was investigated by static light scattering. Bromoform was used as a solvent to minimize multiple scattering. The effect of particle size on the dispersion structure was studied by using particles with two different radii, 141 and 84 nm (diameter ratio = 1.7). For monodisperse systems the scattered intensity depends strongly on the particle volume fraction and the scattering vector. For binary mixtures of these monodisperse particles the scattered intensity is also a strong function of the ratio of large to small particles in the mixture. A model of the structure factor of monodisperse hard spheres matches the experimental scattering data well. For binary mixtures at small fractions of latex 84, the hard sphere model agrees well with the experimental data. At larger fractions of latex 84, some deviations between experimental and calculated values are observed.

The copolymerization of acrylic acid and styrene in a cationic microemulsion made with dodecyltrimethylammonium bromide is reported. Conversion of 60% and fast reaction rates are achieved. The resulting latex is a monodisperse dispersion of spherical particles of 21 nm in radius. The copolymer backbone consists of isolated acrylic acid units randomly distributed among polystyrene blocks.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStyrene polymerization in three-component cationic microemulsionsV. H. Perez-Luna, J. E. Puig, V. M. Castano, B. E. Rodriguez, A. K. Murthy, and E. W. KalerCite this: Langmuir 1990, 6, 6, 1040–1044Publication Date (Print):June 1, 1990Publication History Published online1 May 2002Published inissue 1 June 1990https://pubs.acs.org/doi/10.1021/la00096a002https://doi.org/10.1021/la00096a002research-articleACS PublicationsRequest reuse permissionsArticle Views341Altmetric-Citations94LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

Spontaneous, single-walled, equilibrium vesicles can be prepared from aqueous mixtures of simple, commercially available, single-tailed cationic and anionic surfactants. Vesicle size, surface charge, or permeability can be readily adjusted by varying the ratio of anionic to cationic surfactant. Vesicle formation apparently results from the production of anion-cation surfactant pairs that then act as double-tailed zwitterionic surfactants. These vesicles are quite stable in comparison to conventional vesicles prepared by mechanical disruption of insoluble liquid crystalline dispersions.