Form Of Microdroplets Research Articles

Application and Drying of Protein Drug Microdroplets on Solid Surfaces

A new method to apply small amounts of protein drug solutions in the form of microdroplets to surfaces and to dry them is presented. A robotic dispensing system was used to divide concentrated aqueous protein solutions into microdroplets 20-mL and to place them onto various solid surfaces in a predetermined manner. Afterward, vacuum drying was applied to reduce the residual moisture of the protein/excipient matrix. Optionally, spray coating of the dry microdroplet patterns was carried out to achieve controlled release. Process parameters were studied and optimized for residual moisture, protein stability, and long-term storage stability.

Chromate and Dichromate Electro-Insertion Processes into a N,N,N′,N′-Tetraoctylphenylenediamine Redox Liquid

Ion transfer processes across aqueous vertical bar organic phase boundaries are of considerable importance in biological and analytical chemistry. When driven by a potential applied to the liquid vertical bar liquid interface the ion transfer may be detected as voltammetric response, Here, a potential applied to the electrode vertical bar aqueous electrolyte vertical bar organic oil (N,N,N',N'-tetraoctylphenylenediamine, TOPD) triple interface is employed to drive anion transfer. Upon oxidation of TOPD deposited in the form of microdroplets onto the electrode and immersed in aqueous media, the transfer of monovalent anions (perchlorate) and divalent anions (sulfate, chromate, dichromate) occurs to maintain charge neutrality in the organic oil phase. Sulfate (0.1 M) as a very hydrophilic anion undergoes transfer into the organic phase at a potential positive of 0.4 V (vs. Ag/AgCl) and may be employed as an 'inert' background electrolyte, Chromate is shown to undergo electro-insertion at low concentrations down to 10 muM. Within the oil phase chromate is undergoing condensation to the more stable dichromate.

Fast electrochemical triple-interface processes at boron-doped diamond electrodes

Two important mechanisms for electron transfer processes at boron-doped diamond electrodes involving the oxidation of tetramethylphenylenediamine (TMPD) dissolved in aqueous solution and the oxidation of tetrahexylphenylenediamine (THPD) deposited in the form of microdroplets and immersed into aqueous eletrolyte solution are reported. For TMPD, the first oxidation step in aqueous solution follows the equation:

Extraction of water from a capillary specimen in an acoustic field

Results of a theoretical analysis of experimental data on the acoustic drying of a model capillary sample are presented. It is shown that most of the water is extracted from the sample in the form of microdroplets. The droplet size is evaluated.

Sulfide accumulation and sensing based on electrochemical processes in microdroplets of N1-[4-(dihexylamino)phenyl]-N1,N4,N4-trihexyl-1,4-phenylenediamine

Electroanalytical sulfide detection via oxidation of N1-[4-(dihexylamino)phenyl]-N1,N4,N4-trihexyl-1,4-phenylene diamine (DPTPD) deposited in form of microdroplets onto basal plane pyrolytic graphite electrodes immersed in aqueous 0.1 M NaClO4 containing sulfide is proposed to be associated with two consecutive reversible one electron processes accompanied by ClO4– uptake, sulfide accumulation, and formation of a methylene blue derivative.

Anion Detection by Electro-Insertion intoN,N,N′, N′-Tetrahexyl-Phenylenediamine (THPD) Microdroplets Studied by Voltammetry, EQCM, and SEM Techniques

The electrochemical oxidation and re-reduction of N′,N′,N,N-tetrahexylphenylene diamine (THPD) deposited in form of microdroplets on a basal plane pyrolytic graphite or gold electrode is shown to be a chemically reversible process in the presence of aqueous electrolyte media containing NO3−, SCN−, ClO4−, or PF6−. Sharp voltammetric responses with a mid point potential, Emid, characteristic of the type of anion and its concentration are observed. The oxidation product, an ionic liquid, undergoes rapid ion exchange when the anion of the aqueous electrolyte is exchanged with anions of lower Emid replacing anions of higher Emid. Although the effect of the supporting electrolyte cation in the case of the alkali metals K+, Na+, and Li+ is not significant, a considerable change in the voltammetric peak shape and Emid occurs in the presence of protons. This effect, attributed to the protonation of THPD, is also sensitive to the type of anion present with anions of lower Emid causing more facile protonation. After protonation of THPD, oxidation and re-reduction can be shown to be associated with H+ expulsion and uptake. Deposited onto the rough surface of a gold coated planoconvex quartz crystal oscillator the [THPD+ClO4−]oil deposit can be observed in form of micron-sized droplets in SEM images. A strong frequency response of the crystal oscillator in an electrochemical quartz crystal microbalance experiment associated with the oxidation and re-reduction of THPD can be detected but is not related to changes in mass. Rather, this frequency response may be attributed to changes in the viscosity and/or coverage of the oily deposit.

Redox processes in microdroplets studied by voltammetry, microscopy and ESR spectroscopy: oxidation ofN,N,N′,N′-tetrahexylphenylene diamine deposited on solid electrode surfaces and immersed in aqueous electrolyte solution

Abstract Electrochemical processes in nonhomogeneous media such as emulsions allow the electrolysis of materials of low solubility, which gives rise to new ways of controlling reaction environments, and/or simpler separation of products. However, the mechanistic details of these redox processes are not well understood. Two types of processes may be considered: (i) reactions in the two-phase solution environment coupled by simple mass transport inone phase to the interfacial electron transfer, and (ii) reactions involvingboth liquids in direct contact to the electrode surface (wetting). The latter type of process can be studied separately and is analyzed in this work for the one electron oxidation of the oilN,N,N′,N′-tetrahexylphenylene diamine deposited in the form of microdroplets on basal plane pyrolytic graphite, gold, or siliconized indium tin oxide (ITO) electrodes and immersed in aqueous electrolyte. The bulk conversion of the nonconducting oily material proceeds via the uptake of anions from the aqueous phase and the formation of a dark blue product monitored by voltammetry, optical microscopy, and ESR spectroscopy. The process is extremely sensitive to the type of anion which is electroinserted into the organic phase as is shown for ClO4−, PF6−, Cl−, I−, and OH−. In the case of electroinsertion of hydroxide, a coupled chemical process occurs that can be monitored voltammetrically.

Thermodynamics of Microemulsion Formation

Outlines of complex ternary phase diagrams of cetyltrimethyl ammonium bromide/water/CHCl3, cetylpyridinium chloride/water/CHCl3, sodium bisethylhexyl sulfosuccinate/water/CHCl3, and octylphenoxy polyoxyethylene ether/water/CHCl3systems have been presented. Enthalpies of solution of water-in-oil + amphiphile and oil-in-water + amphiphile media have been calorimetrically determined. Except for cetyltrimethylammonium bromide/water/CHCl3system, all the systems have exhibited thermal inversion for water and oil dispersion near the phase separation point. The surfactant concentration at the inversion point bears a linear correlation with the concentration of the dispersed solvent. The thermodynamics of solubilization of the solvents in the form of microdroplets are presented. The measured heat capacities of all the systems agree very reasonably with the calculated values assuming ideal mixing behavior of the components.

A Calorimetric Determination of Fundamental Properties of Polymer-Dispersed Liquid Crystals

Abstract We have developed a combined calorimetric/electron microscopic technique for determining several fundamental properties of polymer-dispersed liquid crystal (PDLC) films. Calorimetry allows us to determine the solubility limit of liquid crystal in the polymer matrix as well as the fraction of liquid crystal which is dispersed in the form of microdroplets. By combining the calorimetry results with electron microscopy measurements of D, the microdroplet diameter, we are able to calculate the functional relationship between the droplet number density and D. All of these parameters are of considerable importance in assessing the behavior of PDLCs. The usefulness of the method is illustrated by applying it to thermally-cured epoxy-based systems.