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Christopher J Campbell

Publications and source records attributed to Christopher J Campbell.

9 recordsLinked to original sources
PubMed2006

Principles and implementations of dissipative (dynamic) self-assembly.

Dynamic self-assembly (DySA) processes occurring outside of thermodynamic equilibrium underlie many forms of adaptive and intelligent behaviors in natural systems. Relatively little, however, is known about the principles that govern DySA and the ways in which it can be extended to artificial ensembles. This article discusses recent advances in both the theory and the practice of nonequilibrium self-assembly. It is argued that a union of ideas from thermodynamics and dynamic systems' theory can provide a general description of DySA. In parallel, heuristic design rules can be used to construct DySA systems of increasing complexities based on a variety of suitable interactions/potentials on length scales from nanoscopic to macroscopic. Applications of these rules to magnetohydrodynamic DySA are also discussed.

Gold↗
PubMed2006

Testing assumptions about solute concentration dependence in liquid crystal NMR.

The NMR spectra of four solutes, used as probes of liquid crystal orientational order, were analyzed. For each solute, samples were prepared at different solute concentrations, and the concentration dependence was used to extrapolate zero-concentration properties. The mean-field (Maier-Saupe) model when applied to solutes neglects solute-solute interactions and assumes all solutes in a mixed-solute sample see the same average environment. The first assumption is only valid as one approaches zero concentration, while experiments are typically carried out at concentrations between 0 and 10 mol %. The solute concentration dependence has in the past been "scaled out" using an internal solute reference as an orientational standard. We measured the concentration dependence of the orientational order parameter and calculate the corresponding interaction energies based on a mean-field interaction potential for a solute. We find agreement at the 3% level between experiments for different solutes while using (i) the zero-concentration values as solute-dependent orientational references and (ii) scaling to either order parameters or interaction energies; these two scalings gave equivalent but not identical results. We find, too, that errors inherent in the experiment and the calculations will limit attempts to refine the theory to push the comparisons beyond the 2% level.

Journal Article↗
PubMed2005

Nano- and microscopic surface wrinkles of linearly increasing heights prepared by periodic precipitation.

Arrays of surface wrinkles of linearly increasing heights (from tens of nanometers to tens of micrometers) were prepared via a spontaneous reaction-diffusion process based on periodic precipitation. The slopes, dimensions, and positions of the precipitation bands could be controlled precisely by adjusting the concentrations of the participating chemicals as well as the material properties of patterned substrates. Additional control of periodic precipitation by localized UV irradiation allowed for the preparation of discontinuous and curvilinear structures. The nonbinary 3D surface topographies were replicated into poly(dimethylsiloxane), and the applications of replicas in microfluidics, microseparations, and cell biology have been suggested.

Journal Article↗
PubMed2005

Amplification of changes of a thin film's macromolecular structure into macroscopic reaction-diffusion patterns.

A reaction-diffusion process induced from a micronetwork geometry amplifies changes in the molecular structure of a thin gel film into macroscopic readout patterns. When the gel undergoes a helix-to-coil phase transition, the patterns formed by RD switch from symmetry-broken to symmetric ones. Theoretical analysis explains how the system reconfigures internally in response to mass transfer between the applied network and the probed film.

Journal Article↗
PubMed2005

Reactive surface micropatterning by wet stamping.

Hydrogel stamps are used to reactively micropattern various types of substrates. The method, called reactive wet stamping (r-WETS), is general in nature and overcomes several limitations of conventional soft-lithographic techniques. Illustrative applications of r-WETS in surface wettability modification, deposition of metallic microstructures, preparation of supports for electrostatic self-assembly, and multistep reactive patterning are discussed.

Hydrogels↗
PubMed2005

One-step multilevel microfabrication by reaction--diffusion.

A new experimental technique is described that uses reaction--diffusion phenomena as a means of one-step microfabrication of complex, multilevel surface reliefs. Thin films of dry gelatin doped with potassium hexacyanoferrate are chemically micropatterned with a solution of silver nitrate delivered from an agarose stamp. Precipitation reaction between the two salts causes the surface to deform. The mechanism of surface deformation is shown to involve a sequence of reactions, diffusion, and gel swelling/contraction. This mechanism is established experimentally and provides a basis of a theoretical lattice-gas model that allows prediction surface topographies emerging from arbitrary geometries of the stamped features. The usefulness of the technique is demonstrated by using it to rapidly prepare two types of mold for passive microfluidic mixers.

Journal Article↗
PubMed2004

Microfluidic mixers: from microfabricated to self-assembling devices.

This paper begins with a survey of both passive and active microfluidic mixers that have been implemented in recent years. It then describes a micromixing device based on dynamic self-assembly. This device is easy to fabricate and has excellent working characteristics in the continuous-flow mode. The paper concludes with a brief discussion of possible applications of self-assembly in microfluidics.

Complex Mixtures↗
PubMed2003

Bacterial vaginosis in sexually experienced and non-sexually experienced young women entering the military.

OBJECTIVE: To estimate the prevalence of bacterial vaginosis by Nugent Gram stain criteria in a nonclinic national sample of young women entering recruit training; to examine clinical associations with bacterial vaginosis; and to evaluate the performance of a pH test card and Papanicolaou smear against Gram stain as screening tools for bacterial vaginosis. METHODS: A cross-sectional study of 1938 women was conducted. Self-collected vaginal swabs were applied to a colorimetric pH test card and a glass slide for Gram stain evaluation according to the Nugent criteria. Papanicolaou smears and samples for sexually transmitted diseases screening were collected during routine entry pelvic examinations. RESULTS: Bacterial vaginosis prevalence was 27%, with 28% in sexually experienced and 18% in non-sexually experienced women (P = .001). Bacterial vaginosis prevalence was 11% in Asian/Pacific Islanders, which was lower than in other nonwhite ethnic groups (P = .004). Clinically, bacterial vaginosis was directly related to multiple sexual partners (P = .026), self-report of vaginal discharge (P = .001), self-report of vaginal odor (P < .001), and concurrent Chlamydia trachomatis infection (P = .002), and inversely related to hormonal contraceptive use (P = .013). Vaginal discharge did not achieve statistical significance in multivariate analysis. Compared with the Nugent criteria, the sensitivities and specificities for bacterial vaginosis diagnosis were as follows: colorimetric pH test: 72% and 67%; Papanicolaou smear: 72% and 79%, respectively. CONCLUSION: Among these diverse young women, bacterial vaginosis occurs commonly in both sexually experienced and inexperienced young women and differs by race and ethnicity. The pH colorimetric test and Papanicolaou smear performed moderately well as screening tools for bacterial vaginosis. The inverse relationship of bacterial vaginosis with hormonal contraceptive use and its direct relationship with C. trachomatis need further study.

Adolescent↗