Fan Cuia and David J. Pineab Total internal reflection microscopy (TIRM) measures changes in the ... more Fan Cuia and David J. Pineab Total internal reflection microscopy (TIRM) measures changes in the distance between a colloidal particle and a transparent substrate by measuring the intensity of light scattered by the particle when it is illuminated by the evanescent field that is created from light totally internally reflected at the substrate interface. From these measurements, the height-dependent effective potential φ(z) between the colloidal particle and the substrate can be measured. The spatial resolution with which TIRM can resolve the height z and effective potential φ(z) is limited by the intrinsic shot noise of the photon counting process used to measure the scattered light intensity. We develop a model to determine the spatial resolution with which TIRM can measure φ(z) and verify its validity with simulations and experiments. We establish the critical role of shot noise and intensity integration time τ in TIRM measurements of colloidal interaction potentials, which is a t...
Total internal reflection microscopy (TIRM) measures changes in the distance between a colloidal ... more Total internal reflection microscopy (TIRM) measures changes in the distance between a colloidal particle and a transparent substrate by measuring the scattering intensity of the particle illuminated by an evanescent wave.
There is a rich variety of systems in nature which are essentially dense aggregations of particle... more There is a rich variety of systems in nature which are essentially dense aggregations of particle-like structures whose positions vary randomly in space and time. Some common examples include fog, smog, microemulsions, suspensions of glass or polymer microspheres, red blood cells, and ocean particles. In order to understand better and ultimately to gain control over these suspensions it is highly desirable to characterize the structure and dynamics of these systems.
ABSTRACTA method was developed for the production of macroporous oxide materials by using the dro... more ABSTRACTA method was developed for the production of macroporous oxide materials by using the droplets of a nonaqueous emulsion as the templates around which material is deposited through a sol-gel process. Moreover, uniform pores arranged in regular arrays can be obtained by starting with an emulsion of uniform droplets. These droplets first self-assemble into a colloidal crystal after which gelation of the suspending sol-gel mixture captures the ordered structure. After drying and calcination pellets are obtained which contain ordered arrays of spherical pores left behind by the emulsion droplets. The method can be used to make uniform pores in the range from 0.05–5 micrometers in many different materials. We demonstrate the process for titania, silica, and zirconia.
Proceedings of the SPIE - The International Society for Optical Engineering, 2000
We discuss a method for fabricating photonic crystals of closely packed air spheres with diameter... more We discuss a method for fabricating photonic crystals of closely packed air spheres with diameters on the order of 300 nm in a rutile titania matrix. These differ from the air sphere/titania materials reported elsewhere in that the matrix is the high-index rutile phase of titania (n 2.9) as opposed to the low-index anatase phase (n 2.4). We make these materials by a sol-gel process with oil-in-formamide emulsions as templates. The emulsion droplets are stable and have a polydispersity of 15% or less, allowing them to form small colloidal crystallites when concentrated in a titania sol. The oil template can be removed after gelation of the sol and prior to drying, allowing us to produce monolithic samples with few cracks. Calcination at 1000 °C converts the structure to the rutile phase with an average crystallite size of 60 nm. Optical transmission spectra show the presence of a broad minimum at a wavelength of 500 nm for a sample with ordered 200 nm pores.
Holograms of colloidal spheres recorded through holographic video microscopy can be analyzed with... more Holograms of colloidal spheres recorded through holographic video microscopy can be analyzed with the theory of light scattering to measure individual spheres' sizes and refractive indexes with part-per-thousand resolution. This information, in turn, can be interpreted to estimate each sphere's porosity.
We show that coupling between a fast and a slow relaxation time causes the spontaneous formation ... more We show that coupling between a fast and a slow relaxation time causes the spontaneous formation of protrusions in colloids made of cross-linked polymers. The volume of the protrusions can be controlled by adjusting the ratio between the relaxation times. This, in principle, results in particles with levels of anisotropy that can be made "to order".
Rutile titania powders were synthesized via a sol-gel/hydrothermal process using nitric acid as t... more Rutile titania powders were synthesized via a sol-gel/hydrothermal process using nitric acid as the catalyst. A molar acid to alkoxide ratio of 10 and a water to alkoxide molar ratio of 250 produced 100% rutile powders when precipitated below 45 °C. Higher temperatures yielded initially either anatase or mixtures of anatase and rutile. Spherulitic growth produced cauliflower-shaped agglomerates with a mean size of 760 nm. The agglomerates could be broken apart into approximately 100-nm large broomlike agglomerates via a dissolution and reprecipitation process when reacted with approximately 2.4 molar nitric acid. Transmission electron microscopy observations showed that the broomlike agglomerate consisted of linear clusters of rodlike agglomerates composed of crystallographically aligned, primary particles approximately 4 nm in size.
Porous silica, niobia, and titania with three-dimensional structures patterned over multiple leng... more Porous silica, niobia, and titania with three-dimensional structures patterned over multiple length scales were prepared by combining micromolding, polystyrene sphere templating, and cooperative assembly of inorganic sol-gel species with amphiphilic triblock copolymers. The resulting materials show hierarchical ordering over several discrete and tunable length scales ranging from 10 nanometers to several micrometers. The respective ordered structures can be independently modified by choosing different mold patterns, latex spheres, and block copolymers. The examples presented demonstrate the compositional and structural diversities that are possible with this simple approach.
The wavelength-dependent diffuse transmission through a monodisperse colloidal suspension is show... more The wavelength-dependent diffuse transmission through a monodisperse colloidal suspension is shown to provide wave-vector-dependent information about the colloid structure factor. Experiments demonstrate that the spectral fingerprint can be used to distinguish quantitatively samples of different particle sizes, different concentrations, and different interparticle interactions.
We have investigated the equilibrium compositions and structures of the phases of nearly-hardsphe... more We have investigated the equilibrium compositions and structures of the phases of nearly-hardsphere binary colloids and obtained experimental phase diagrams. Aqueous dispersions of chargestabilized polystyrene spheres were studied in the hard-sphere limit, with sphere-diameter ratios ranging from 2 to 12 and total volume fractions less than 0.4. At sufficiently high volume fractions, the samples separated into two phases. One phase, consisting primarily of small spheres, is a disordered fluid. In the other phase, the large spheres form an ordered crystalline solid which is permeated by a disordered fluid of small spheres. Previously reported crystallites on the surface of the sample cell were demonstrated to have the same structure as the bulk crystals and are assumed to be a wetting of the bulk phase. A simple model of the bulk phases is described and free energies calculated. The predicted phase diagrams agree closely .with the results of computer simulations and with our experimental results.
† Electronic supplementary information (ESI) available: 1 figure showing crystal growth by coales... more † Electronic supplementary information (ESI) available: 1 figure showing crystal growth by coalescence, 2 movies showing crystal nucleation and melting. Supplementary text on particle shape analysis and particle tracking. See
Model colloids composed of two widely separated sizes of polystyrene spheres are studied at high ... more Model colloids composed of two widely separated sizes of polystyrene spheres are studied at high volume fractions using an optical, multiple-scattering technique. These measurements probe hydrodynamic forces between unlike particles, as well as static, structural predictions made using the Percus-Yevick approximation. The dynamic data corroborate currently available hydrodynamic theories on very short length scales; the dynamic data also reveal a new, experimentally accessible range of intermediate length scales which currently available theories cannot explain.
We investigate the phase diagram of mixtures of charge stabilized polystyrene spheres of two diff... more We investigate the phase diagram of mixtures of charge stabilized polystyrene spheres of two different sizes in the hard-sphere limit. We observe bulk phase separation into two disordered phases and find a new ordered phase located on the cell walls. The ordered phase occurs at volume fractions as low as 0.2, much less than the value of 0.49 for hard-sphere freezing in monodisperse suspensions, and is qualitatively explained with simple geometric arguments.
We discuss localization phenomena in multilayer films doped with scattering particles. If the fil... more We discuss localization phenomena in multilayer films doped with scattering particles. If the films exhibit a particular type of transmission resonance then above a critical frequency waves in the sample can decay as a power law rather than exponentially. This phenomenon is independent of the scattering strength of the particles, in stark contrast to previous work. We find that this phenomenon has many similarities to a second order phase transition. This work points to interesting avenues in the study of waves in anisotropic disordered media.
DNA molecules provide what is probably the most iconic example of self-replication-the ability of... more DNA molecules provide what is probably the most iconic example of self-replication-the ability of a system to replicate, or make copies of, itself. In living cells the process is mediated by enzymes and occurs autonomously, with the number of replicas increasing exponentially over time without the need for external manipulation. Self-replication has also been implemented with synthetic systems, including RNA enzymes designed to undergo self-sustained exponential amplification 1-5. An exciting next step would be to use self-replication in materials fabrication, which requires robust and general systems capable of copying and amplifying functional materials or structures. Here we report a first development in this direction, using DNA tile motifs that can recognize and bind complementary tiles in a pre-programmed fashion. We first design tile motifs so they form a seven-tile seed sequence, then use the seeds to instruct the formation of a first generation of complementary seven-tile daughter sequences, and finally use the daughters to instruct the formation of seven-tile granddaughter sequences that are identical to the initial seed sequences. Considering that DNA is a functional material that can organize itself and other molecules into useful structures 6-13 , our findings raise the tantalizing prospect that we may one day be able to realize self-replicating materials with various patterns or useful functions. Nucleic acids comprise the genetic material of all living organisms, with the ordered pattern of bases in the DNA double helix readily copied by an enzymatic process that leads to semiconservative replication within the cell 14,15. The replication process exploits the complementarity of the four-letter code made of the bases within the linear DNA double Users may view, print, copy, download and text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:
Fan Cuia and David J. Pineab Total internal reflection microscopy (TIRM) measures changes in the ... more Fan Cuia and David J. Pineab Total internal reflection microscopy (TIRM) measures changes in the distance between a colloidal particle and a transparent substrate by measuring the intensity of light scattered by the particle when it is illuminated by the evanescent field that is created from light totally internally reflected at the substrate interface. From these measurements, the height-dependent effective potential φ(z) between the colloidal particle and the substrate can be measured. The spatial resolution with which TIRM can resolve the height z and effective potential φ(z) is limited by the intrinsic shot noise of the photon counting process used to measure the scattered light intensity. We develop a model to determine the spatial resolution with which TIRM can measure φ(z) and verify its validity with simulations and experiments. We establish the critical role of shot noise and intensity integration time τ in TIRM measurements of colloidal interaction potentials, which is a t...
Total internal reflection microscopy (TIRM) measures changes in the distance between a colloidal ... more Total internal reflection microscopy (TIRM) measures changes in the distance between a colloidal particle and a transparent substrate by measuring the scattering intensity of the particle illuminated by an evanescent wave.
There is a rich variety of systems in nature which are essentially dense aggregations of particle... more There is a rich variety of systems in nature which are essentially dense aggregations of particle-like structures whose positions vary randomly in space and time. Some common examples include fog, smog, microemulsions, suspensions of glass or polymer microspheres, red blood cells, and ocean particles. In order to understand better and ultimately to gain control over these suspensions it is highly desirable to characterize the structure and dynamics of these systems.
ABSTRACTA method was developed for the production of macroporous oxide materials by using the dro... more ABSTRACTA method was developed for the production of macroporous oxide materials by using the droplets of a nonaqueous emulsion as the templates around which material is deposited through a sol-gel process. Moreover, uniform pores arranged in regular arrays can be obtained by starting with an emulsion of uniform droplets. These droplets first self-assemble into a colloidal crystal after which gelation of the suspending sol-gel mixture captures the ordered structure. After drying and calcination pellets are obtained which contain ordered arrays of spherical pores left behind by the emulsion droplets. The method can be used to make uniform pores in the range from 0.05–5 micrometers in many different materials. We demonstrate the process for titania, silica, and zirconia.
Proceedings of the SPIE - The International Society for Optical Engineering, 2000
We discuss a method for fabricating photonic crystals of closely packed air spheres with diameter... more We discuss a method for fabricating photonic crystals of closely packed air spheres with diameters on the order of 300 nm in a rutile titania matrix. These differ from the air sphere/titania materials reported elsewhere in that the matrix is the high-index rutile phase of titania (n 2.9) as opposed to the low-index anatase phase (n 2.4). We make these materials by a sol-gel process with oil-in-formamide emulsions as templates. The emulsion droplets are stable and have a polydispersity of 15% or less, allowing them to form small colloidal crystallites when concentrated in a titania sol. The oil template can be removed after gelation of the sol and prior to drying, allowing us to produce monolithic samples with few cracks. Calcination at 1000 °C converts the structure to the rutile phase with an average crystallite size of 60 nm. Optical transmission spectra show the presence of a broad minimum at a wavelength of 500 nm for a sample with ordered 200 nm pores.
Holograms of colloidal spheres recorded through holographic video microscopy can be analyzed with... more Holograms of colloidal spheres recorded through holographic video microscopy can be analyzed with the theory of light scattering to measure individual spheres' sizes and refractive indexes with part-per-thousand resolution. This information, in turn, can be interpreted to estimate each sphere's porosity.
We show that coupling between a fast and a slow relaxation time causes the spontaneous formation ... more We show that coupling between a fast and a slow relaxation time causes the spontaneous formation of protrusions in colloids made of cross-linked polymers. The volume of the protrusions can be controlled by adjusting the ratio between the relaxation times. This, in principle, results in particles with levels of anisotropy that can be made "to order".
Rutile titania powders were synthesized via a sol-gel/hydrothermal process using nitric acid as t... more Rutile titania powders were synthesized via a sol-gel/hydrothermal process using nitric acid as the catalyst. A molar acid to alkoxide ratio of 10 and a water to alkoxide molar ratio of 250 produced 100% rutile powders when precipitated below 45 °C. Higher temperatures yielded initially either anatase or mixtures of anatase and rutile. Spherulitic growth produced cauliflower-shaped agglomerates with a mean size of 760 nm. The agglomerates could be broken apart into approximately 100-nm large broomlike agglomerates via a dissolution and reprecipitation process when reacted with approximately 2.4 molar nitric acid. Transmission electron microscopy observations showed that the broomlike agglomerate consisted of linear clusters of rodlike agglomerates composed of crystallographically aligned, primary particles approximately 4 nm in size.
Porous silica, niobia, and titania with three-dimensional structures patterned over multiple leng... more Porous silica, niobia, and titania with three-dimensional structures patterned over multiple length scales were prepared by combining micromolding, polystyrene sphere templating, and cooperative assembly of inorganic sol-gel species with amphiphilic triblock copolymers. The resulting materials show hierarchical ordering over several discrete and tunable length scales ranging from 10 nanometers to several micrometers. The respective ordered structures can be independently modified by choosing different mold patterns, latex spheres, and block copolymers. The examples presented demonstrate the compositional and structural diversities that are possible with this simple approach.
The wavelength-dependent diffuse transmission through a monodisperse colloidal suspension is show... more The wavelength-dependent diffuse transmission through a monodisperse colloidal suspension is shown to provide wave-vector-dependent information about the colloid structure factor. Experiments demonstrate that the spectral fingerprint can be used to distinguish quantitatively samples of different particle sizes, different concentrations, and different interparticle interactions.
We have investigated the equilibrium compositions and structures of the phases of nearly-hardsphe... more We have investigated the equilibrium compositions and structures of the phases of nearly-hardsphere binary colloids and obtained experimental phase diagrams. Aqueous dispersions of chargestabilized polystyrene spheres were studied in the hard-sphere limit, with sphere-diameter ratios ranging from 2 to 12 and total volume fractions less than 0.4. At sufficiently high volume fractions, the samples separated into two phases. One phase, consisting primarily of small spheres, is a disordered fluid. In the other phase, the large spheres form an ordered crystalline solid which is permeated by a disordered fluid of small spheres. Previously reported crystallites on the surface of the sample cell were demonstrated to have the same structure as the bulk crystals and are assumed to be a wetting of the bulk phase. A simple model of the bulk phases is described and free energies calculated. The predicted phase diagrams agree closely .with the results of computer simulations and with our experimental results.
† Electronic supplementary information (ESI) available: 1 figure showing crystal growth by coales... more † Electronic supplementary information (ESI) available: 1 figure showing crystal growth by coalescence, 2 movies showing crystal nucleation and melting. Supplementary text on particle shape analysis and particle tracking. See
Model colloids composed of two widely separated sizes of polystyrene spheres are studied at high ... more Model colloids composed of two widely separated sizes of polystyrene spheres are studied at high volume fractions using an optical, multiple-scattering technique. These measurements probe hydrodynamic forces between unlike particles, as well as static, structural predictions made using the Percus-Yevick approximation. The dynamic data corroborate currently available hydrodynamic theories on very short length scales; the dynamic data also reveal a new, experimentally accessible range of intermediate length scales which currently available theories cannot explain.
We investigate the phase diagram of mixtures of charge stabilized polystyrene spheres of two diff... more We investigate the phase diagram of mixtures of charge stabilized polystyrene spheres of two different sizes in the hard-sphere limit. We observe bulk phase separation into two disordered phases and find a new ordered phase located on the cell walls. The ordered phase occurs at volume fractions as low as 0.2, much less than the value of 0.49 for hard-sphere freezing in monodisperse suspensions, and is qualitatively explained with simple geometric arguments.
We discuss localization phenomena in multilayer films doped with scattering particles. If the fil... more We discuss localization phenomena in multilayer films doped with scattering particles. If the films exhibit a particular type of transmission resonance then above a critical frequency waves in the sample can decay as a power law rather than exponentially. This phenomenon is independent of the scattering strength of the particles, in stark contrast to previous work. We find that this phenomenon has many similarities to a second order phase transition. This work points to interesting avenues in the study of waves in anisotropic disordered media.
DNA molecules provide what is probably the most iconic example of self-replication-the ability of... more DNA molecules provide what is probably the most iconic example of self-replication-the ability of a system to replicate, or make copies of, itself. In living cells the process is mediated by enzymes and occurs autonomously, with the number of replicas increasing exponentially over time without the need for external manipulation. Self-replication has also been implemented with synthetic systems, including RNA enzymes designed to undergo self-sustained exponential amplification 1-5. An exciting next step would be to use self-replication in materials fabrication, which requires robust and general systems capable of copying and amplifying functional materials or structures. Here we report a first development in this direction, using DNA tile motifs that can recognize and bind complementary tiles in a pre-programmed fashion. We first design tile motifs so they form a seven-tile seed sequence, then use the seeds to instruct the formation of a first generation of complementary seven-tile daughter sequences, and finally use the daughters to instruct the formation of seven-tile granddaughter sequences that are identical to the initial seed sequences. Considering that DNA is a functional material that can organize itself and other molecules into useful structures 6-13 , our findings raise the tantalizing prospect that we may one day be able to realize self-replicating materials with various patterns or useful functions. Nucleic acids comprise the genetic material of all living organisms, with the ordered pattern of bases in the DNA double helix readily copied by an enzymatic process that leads to semiconservative replication within the cell 14,15. The replication process exploits the complementarity of the four-letter code made of the bases within the linear DNA double Users may view, print, copy, download and text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:
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Papers by David J Pine