Complex colloids by the emulsion solvent evaporation process

In this thesis, different complex colloids were prepared by the process of solvent evaporation from emulsion droplets (SEED). The term “complex” is used to include both an addressable functionality as well as the heterogeneous nature of the colloids.Firstly, as the SEED process was used throughout the thesis, its mechanism especially in regard to coalescence was investigated,. A wide variety of different techniques was employed to study the coalescence of nanodroplets during the evaporation of the solvent. Techniques such as DLS or FCS turned out not to be suitable methods to determine droplet coalescence because of their dependence on dilution. Thus, other methods were developed. TEM measurements were conducted on mixed polymeric emulsions with the results pointing to an absence of coalescence. However, these results were not quantifiable. FRET measurements on mixed polymeric emulsions also indicated an absence of coalescence. Again the results were not quantifiable. The amount of coalescence taking place was then quantified by the application of DC-FCCS. This method also allowed for measuring coalescence in other processes such as the miniemulsion polymerization or the polycondensation reaction on the interface of the droplets. By simulations it was shown that coalescence is not responsible for the usually observed broad size distribution of the produced particles. Therefore, the process itself, especially the emulsification step, needs to be improved to generate monodisperse colloids.rnThe Janus morphology is probably the best known among the different complex morphologies of nanoparticles. With the help of functional polymers, it was possible to marry click-chemistry to Janus particles. A large library of functional polymers was prepared by copolymerization and subsequent post-functionalization or by ATRP. The polymers were then used to generate Janus particles by the SEED process. Both dually functionalized Janus particles and particles with one functionalized face could be obtained. The latter were used for the quantification of functional groups on the surface of the Janus particles. For this, clickable fluorescent dyes were synthesized. The degree of functionality of the polymers was found to be closely mirrored in the degree of functionality of the surface. Thus, the marriage of click-chemistry to Janus particles was successful.Another complex morphology besides Janus particles are nanocapsules. Stimulus-responsive nanocapsules that show triggered release are a highly demanding and interesting system, as nanocapsules have promising applications in drug delivery and in self-healing materials. To achieve heterogeneity in the polymer shell, the stimulus-responsive block copolymer PVFc-b-PMMA was employed for the preparation of the capsules. The phase separation of the two blocks in the shell of the capsules led to a patchy morphology. These patches could then be oxidized resulting in morphology changes. In addition, swelling occurred because of the hydrophobic to hydrophilic transition of the patches induced by the oxidation. Due to the swelling, an encapsulated payload could diffuse out of the capsules, hence release was achieved.The concept of using block copolymers responsive to one stimulus for the preparation of stimulus-responsive capsules was extended to block copolymers responsive to more than one stimulus. Here, a block copolymer responsive to oxidation and a pH change as well as a block copolymer responsive to a pH change and temperature were studied in detail. The release from the nanocapsules could be regulated by tuning the different stimuli. In addition, by encapsulating stimuli-responsive payloads it was possible to selectively release a payload upon one stimulus but not upon the other one.In conclusion, the approaches taken in the course of this thesis demonstrate the broad applicability and usefulness of the SEED process to generate complex colloids. In addition, the experimental techniques established such as DC-FCCS will provide further insight into other research areas as well.

Monitoring kinetic processes in polymeric colloids by fluorescence correlation spectroscopy

Polymerbasierte Kolloide mit Groen im Nanometerbereich werden als aussichts- reiche Kandidaten fur die Verkapselung und den Transport von pharmazeutischen Wirkstoen angesehen. Daher ist es wichtig die physikalischen Prozesse, die die Bil- dung, Struktur und kinetische Stabilitat der polymerbasierten Kolloide beein ussen, besser zu verstehen. Allerdings ist die Untersuchung dieser Prozesse fur nanome- tergroe Objekte kompliziert und erfordert fortgeschrittene Techniken. In dieser Arbeit beschreibe ich Untersuchungen, bei denen Zwei-Farben-Fluoreszenzkreuz- korrelationsspektroskopie (DC FCCS) genutzt wurde, um Informationen uber die Wechselwirkung und den Austausch von dispergierten, nanometergroen Kolloiden zu bekommen. Zunachst habe ich den Prozess der Polymernanopartikelherstellung aus Emul- sionstropfen untersucht, welcher einen der am haugsten angewendeten Prozesse der Nanopartikelformulierung darstellt. Ich konnte zeigen, dass mit DC FCCS eindeutig und direkt Koaleszenz zwischen Emulsionstropfen gemessen werden kann. Dies ist von Interesse, da Koaleszenz als Hauptgrund fur die breite Groenverteilung der nalen Nanopartikel angesehen wird. Weiterhin habe ich den Austausch von Mizellen bildenden Molekulen zwischen amphiphilen Diblock Kopolymermizellen untersucht. Als Modellsystem diente ein Linear-Burste Block Kopolymer, welches Mizellen mit einer dichten und kurzen Korona bildet. Mit Hilfe von DC FCCS konnte der Austausch in verschiedenen Losungsmitteln und bei verschiedenen Temperaturen beobachtet werden. Ich habe herausgefunden, dass in Abhangigkeit der Qualitat des Losungsmittels die Zeit des Austausches um Groenordnungen verschoben werden kann, was eine weitreichende Einstellung der Austauschkinetik ermoglicht. Eine Eigenschaft die all diese Kolloide gemeinsam haben ist ihre Polydispersitat. Im letzten Teil meiner Arbeit habe ich am Beispiel von Polymeren als Modellsystem untersucht, welchen Eekt Polydispersitat und die Art der Fluoreszenzmarkierung auf FCS Experimente haben. Eine Anpassung des klassischen FCS Modells kann die FCS Korrelationskurven dieser Systeme beschreiben. Die Richtigkeit meines Ansatzes habe ich mit dem Vergleich zur Gel-Permeations-Chromatographie und Brownschen Molekulardynamiksimulationen bestatigt.

Crystalloids versus colloids for goal-directed fluid therapy in major surgery

INTRODUCTION: Perioperative hypovolemia arises frequently and contributes to intestinal hypoperfusion and subsequent postoperative complications. Goal-directed fluid therapy might reduce these complications. The aim of this study was to compare the effects of goal-directed administration of crystalloids and colloids on the distribution of systemic, hepatosplanchnic, and microcirculatory (small intestine) blood flow after major abdominal surgery in a clinically relevant pig model. METHODS: Twenty-seven pigs were anesthetized and mechanically ventilated and underwent open laparotomy. They were randomly assigned to one of three treatment groups: the restricted Ringer lactate (R-RL) group (n = 9) received 3 mL/kg per hour of RL, the goal-directed RL (GD-RL) group (n = 9) received 3 mL/kg per hour of RL and intermittent boluses of 250 mL of RL, and the goal-directed colloid (GD-C) group (n = 9) received 3 mL/kg per hour of RL and boluses of 250 mL of 6% hydroxyethyl starch (130/0.4). The latter two groups received a bolus infusion when mixed venous oxygen saturation was below 60% ('lockout' time of 30 minutes). Regional blood flow was measured in the superior mesenteric artery and the celiac trunk. In the small bowel, microcirculatory blood flow was measured using laser Doppler flowmetry. Intestinal tissue oxygen tension was measured with intramural Clark-type electrodes. RESULTS: After 4 hours of treatment, arterial blood pressure, cardiac output, mesenteric artery flow, and mixed oxygen saturation were significantly higher in the GD-C and GD-RL groups than in the R-RL group. Microcirculatory flow in the intestinal mucosa increased by 50% in the GD-C group but remained unchanged in the other two groups. Likewise, tissue oxygen tension in the intestine increased by 30% in the GD-C group but remained unchanged in the GD-RL group and decreased by 18% in the R-RL group. Mesenteric venous glucose concentrations were higher and lactate levels were lower in the GD-C group compared with the two crystalloid groups. CONCLUSIONS: Goal-directed colloid administration markedly increased microcirculatory blood flow in the small intestine and intestinal tissue oxygen tension after abdominal surgery. In contrast, goal-directed crystalloid and restricted crystalloid administrations had no such effects. Additionally, mesenteric venous glucose and lactate concentrations suggest that intestinal cellular substrate levels were higher in the colloid-treated than in the crystalloid-treated animals. These results support the notion that perioperative goal-directed therapy with colloids might be beneficial during major abdominal surgery.

Brownian flocculation of polymer colloids in the presence of a secondary minimum

Most analyses of Brownian flocculation apply to conditions where London–van der Waals attractive forces cause particles to be strongly bound in a deep interparticle potential well. In this paper, results are reported that show the interaction between primary- and secondary-minimum flocculation when the interparticle potential curve reflects both attractive and electrostatic repulsive forces. The process is highly time-dependent because of transfer of particles from secondary- to primary-minimum flocculation. Essential features of the analysis are corroborated by experiments with 0.80-μm polystyrene spheres suspended in aqueous solutions of NaCl over a range of ionic strengths. In all cases, experiments were restricted to the initial stage of coagulation, where singlets and doublets predominate.

Phase diagram of a polydisperse soft-spheres model for liquids and colloids

The phase diagram of soft spheres with size dispersion is studied by means of an optimized Monte Carlo algorithm which allows us to equilibrate below the kinetic glass transition for all size distributions. The system ubiquitously undergoes a first-order freezing transition. While for a small size dispersion the frozen phase has a crystalline structure, large density inhomogeneities appear in the highly disperse systems. Studying the interplay between the equilibrium phase diagram and the kinetic glass transition, we argue that the experimentally found terminal polydispersity of colloids is a purely kinetic phenomenon.

Quantum Dot-Sensitized Solar Cells Based on Directly Adsorbed Zinc Copper Indium Sulfide Colloids

Heavy metal-based quantum dots (QDs) have demonstrated to behave as efficient sensitizers in QD-sensitized solar cells (QDSSCs), as attested by the countless works and encouraging efficiencies reported so far. However, their intrinsic toxicity has arisen as a major issue for the prospects of commercialization. Here, we examine the potential of environmentally friendly zinc copper indium sulfide (ZCIS) QDs for the fabrication of liquid-junction QDSSCs by means of photoelectrochemical measurements. A straightforward approach to directly adsorb ZCIS QDs on TiO2 from a colloidal dispersion is presented. Incident photon-to-current efficiency (IPCE) spectra of sensitized photoanodes show a marked dependence on the adsorption time, with longer times leading to poorer performances. Cyclic voltammograms point to a blockage of the channels of the mesoporous TiO2 film by the agglomeration of QDs as the main reason for the decrease in efficiency. Photoanodes were also submitted to the ZnS treatment. Its effects on electron recombination with the electrolyte are analyzed through electrochemical impedance spectroscopy and photopotential measurements. The corresponding results bring out the role of the ZnS coating as a barrier layer preventing electron leakage toward the electrolyte, as argued in other QD-sensitized systems. The beneficial effect of the ZnS coating is ultimately reflected on the power conversion efficiency of complete devices, reaching values of 2 %. In a more general vein, through these findings, we aim to call the attention to the potentiality of this quaternary alloy, virtually unexplored as a light harvester for sensitized devices.

An introduction to the physics and chemistry of colloids,

At head of title: Text-book of chemical research and engineering.

The chemistry of colloids and some technical applications;

"In this edition the main features of the book remain unaltered, although a considerable amount of new material has been added."--Pref.

Structure and mechanics of active colloids

11 pages Acknowledgments MCM thanks Xingbo Yang and Lisa Manning for their contribution to some aspects of the work reviewed here and for fruitful discussions. MCM was supported by NSF-DMR-305184. MCM and AP acknowledge support by the NSF IGERT program through award NSF-DGE-1068780. MCM, AP and DY were additionally supported by the Soft Matter Program at Syracuse University. AP acknowledges use of the Syracuse University HTC Campus Grid which is supported by NSF award ACI-1341006. YF was supported by NSF grant DMR-1149266 and the Brandeis Center for Bioinspired Soft Materials, an NSF MRSEC, DMR-1420382.

Structure and mechanics of active colloids

11 pages Acknowledgments MCM thanks Xingbo Yang and Lisa Manning for their contribution to some aspects of the work reviewed here and for fruitful discussions. MCM was supported by NSF-DMR-305184. MCM and AP acknowledge support by the NSF IGERT program through award NSF-DGE-1068780. MCM, AP and DY were additionally supported by the Soft Matter Program at Syracuse University. AP acknowledges use of the Syracuse University HTC Campus Grid which is supported by NSF award ACI-1341006. YF was supported by NSF grant DMR-1149266 and the Brandeis Center for Bioinspired Soft Materials, an NSF MRSEC, DMR-1420382.

Phase behavior and far-from-equilibrium gelation in charged attractive colloids

In this Rapid Communication we demonstrate the applicability of an augmented Gibbs ensemble Monte Carlo approach for the phase behavior determination of model colloidal systems with short-ranged depletion attraction and long-ranged repulsion. This technique allows for a quantitative determination of the phase boundaries and ground states in such systems. We demonstrate that gelation may occur in systems of this type as the result of arrested microphase separation, even when the equilibrium state of the system is characterized by compact microphase structures.