Analysis of Inorganic Polyphosphates by Capillary Gel Electrophoresis

This paper describes the development of a method that uses capillary gel electrophoresis (CGE) to analyze mixtures of inorganic polyphosphate ((P$_i$)$_n$). Resolution of (P$_i$)$_n$ on the basis of n, the number of residues of dehydrated phosphate, is accomplished by CGE using capillaries filled with solutions of poly(N,N-dimethylacrylamide) (PDMA) and indirect detection by the UV absorbance of a chromophore, terephthalate, added to the running buffer. The method is capable of resolving peaks representing (P$_i$)$_n$ with n up to 70; preparation and use of authentic standards enables the identification of peaks for (P$_i$)$_n$ with n = 1−10. The main advantages of this method over previously reported methods for analyzing mixtures of (P$_i$)$_n$ (e.g., gel electrophoresis, CGE using polyacrylamide-filled capillaries) are its resolution, convenience, and reproducibility; gel-filled capillaries are easily regenerated by pumping in fresh, low-viscosity solutions of PDMA. The resolution is comparable to that of ion-exchange chromatography and detection of (P$_i$)$_n$ by suppressed conductivity. The method is useful for analyzing (P$_i$)$_n$ generated by the dehydration of P$_i$ at low temperature (125−140 °C) with urea, in a reaction that may have been important in prebiotic chemistry. The method should also be useful for characterizing mixtures of other anionic, oligomeric, or polymeric species without an intrinsic chromophore (e.g., sulfated polysaccharides, oligomeric phospho-diesters).Chemistry and Chemical Biolog

Patterned Paper as a Template for the Delivery of Reactants in the Fabrication of Planar Materials

This account reviews the use of templates, fabricated by patterning paper, for the delivery of aqueous solutions of reactants (predominantly, ions) in the preparation of structured, thin materials (e.g., films of ionotropic hydrogels). In these methods, a patterned sheet of paper transfers an aqueous solution of reagent to a second phase—either solid or liquid—brought into contact with the template; this process can form solid structures with thicknesses that are typically ≤1.5 mm. The shape of the template and the pattern of a hydrophobic barrier on the paper control the shape of the product, in its plane, by restricting the delivery of the reagent in two dimensions. The concentration of the reagents, and the duration that the template remains in contact with the second phase, control growth in the third dimension (i.e., thickness). The method is especially useful in fabricating shaped films of ionotropic hydrogels (e.g., calcium alginate ) by controlling the delivery of solutions of multivalent cations to solutions of anionic polymers. The templates can also be used to direct reactions that generate patterns of solid precipitates within sheets of paper. This review examines applications of the method for: (i) patterning bacteria in two dimensions within a hydrogel film, (ii) manipulating hydrogel films and sheets of paper magnetically, and (iii) generating dynamic 3-D structures (e.g., a cylinder of rising bubbles of O$_2$) from sheets of paper with 2-D patterns of a catalyst (e.g., Pd$^0$) immersed in appropriate reagents (e.g., 1% H$_2$O$_2$ in water).Chemistry and Chemical Biolog

STRETCHABLE CONDUCTIVE COMPOSITES FOR USE IN SOFT DEVICES

An elastically-deformable, conductive composite using elastomers and conductive fibers and simple fabrication procedures is provided. Conductive elastomeric composites offer low resistance to electrical current and are elastic over large (\u3e25%) extensional strains. They can be easily interfaced/built into structures fabricated from elastomeric polymers

Microfabrication inside capillaries using multiphase laminar flow patterning

The reaction of species in solutions flowing laminarly (without turbulent mixing) inside capillaries was used as the basis for a broadly applicable method of microfabrication. In this method, patterning occurs as a result of transport of reactive species to interfaces within the capillary by laminar flow. A wide range of chemistries can be used to generate structures with feature sizes of less than 5 micrometers and with spatial localization to within 5 micrometers. The method is applicable to the patterning of metals, organic polymers, inorganic crystals, and ceramics on the inner walls of preformed capillaries, using both additive and subtractive processes

Contact De-electrification of Electrostatically Charged Polymers

The contact electrification of insulating organic polymers is still incompletely understood, in part because multiple fundamental mechanisms may contribute to the movement of charge. This study describes a mechanism previously unreported in the context of contact electrification: that is, “contact de-electrification”, a process in which polymers charged to the same polarity discharge on contact. Both positively charged polymeric beads, e.g., polyamide 6/6 (Nylon) and polyoxymethylene (Delrin), and negatively charged polymeric beads, e.g., polytetrafluoroethylene (Teflon) and polyamide-imide (Torlon), discharge when the like-charged beads are brought into contact. The beads (both with charges of ±20 μC/m2, or 100 charges/μm2) discharge on contact regardless of whether they are made of the same material, or of different materials. Discharge is rapid: discharge of flat slabs of like-charged Nylon and Teflon pieces is completed on a single contact (3 s). The charge lost from the polymers during contact de-electrification transfers onto molecules of gas in the atmosphere. When like-charged polymers are brought into contact, the increase in electric field at the point of contact exceeds the dielectric breakdown strength of the atmosphere and ionizes molecules of the gas; this ionization thus leads to discharge of the polymers. The detection (using a Faraday cup) of charges transferred to the cup by the ionized gas is compatible with the mechanism. Contact de-electrification occurs for different polymers and in atmospheres with different values of dielectric breakdown strength (helium, argon, oxygen, carbon dioxide, nitrogen, and sulfur hexafluoride): the mechanism thus appears to be general.Chemistry and Chemical Biolog

Electric winds driven by time oscillating corona discharges

We investigate the formation of steady gas flows—so-called electric winds—created by point-plane corona discharges driven by time oscillating (ac) electric fields. By varying the magnitude and frequency of the applied field, we identify two distinct scaling regimes: (i) a low frequency (dc) regime and (ii) a high frequency (ac) regime. These experimental observations are reproduced and explained by a theoretical model describing the transport and recombination of ions surrounding the discharge and their contribution to the measured wind velocity. The two regimes differ in the spatial distribution of ions and in the process by which ions are consumed. Interestingly, we find that ac corona discharges generate strong electric forces localized near the tip of the point electrode, while dc corona discharges generate weaker forces distributed throughout the interelectrode region. Consequently, the velocity of the electric winds (>1 m/s) generated by ac discharges is largely independent of the position of the counter electrode. The unified theoretical description of dc and ac electric winds presented here reconciles previous observations of winds driven by dc corona and ac dielectric barrier discharges; insights from the model should also prove useful in the design of other plasma actuators.Chemistry and Chemical Biolog

Elastomeric Origami: Programmable Paper-Elastomer Composites as Pneumatic Actuators

The development of soft pneumatic actuators based on composites consisting of elastomers with embedded sheet or fiber structures (e.g., paper or fabric) that are flexible but not extensible is described. On pneumatic inflation, these actuators move anisotropically, based on the motions accessible by their composite structures. They are inexpensive, simple to fabricate, light in weight, and easy to actuate. This class of structure is versatile: the same principles of design lead to actuators that respond to pressurization with a wide range of motions (bending, extension, contraction, twisting, and others). Paper, when used to introduce anisotropy into elastomers, can be readily folded into 3D structures following the principles of origami; these folded structures increase the stiffness and anisotropy of the elastomeric actuators, while being light in weight. These soft actuators can manipulate objects with moderate performance; for example, they can lift loads up to 120 times their weight. They can also be combined with other components, for example, electrical components, to increase their functionality.Chemistry and Chemical Biolog

Integration of paper-based microfluidic devices with commercial electrochemical readers

The combination of simple Electrochemical Micro-Paper-based Analytical Devices (E$\mu$PADs) with commercially available glucometers allows rapid, quantitative electrochemical analysis of a number of compounds relevant to human health (e.g., glucose, cholesterol, lactate, and alcohol) in blood or urine.Chemistry and Chemical Biolog