39 research outputs found
Metallization of colloidal crystals
Colloidal crystals formed by size-asymmetric binary particles co-assemble
into a wide variety of colloidal compounds with lattices akin to ionic
crystals. Recently, a transition from a compound phase with a sublattice of
small particles to a metal-like phase in which the small particles are
delocalized has been predicted computationally and observed experimentally. In
this colloidal metallic phase, the small particles roam the crystal maintaining
the integrity of the lattice of large particles, as electrons do in metals. A
similar transition also occurs in superionic crystals, termed sublattice
melting. Here, we use energetic principles and a generalized molecular dynamics
model of a binary system of functionalized nanoparticles to analyze the
transition to sublattice delocalization in different co-assembled crystal
phases as a function of T, number of grafted chains on the small particles, and
number ratio between the small and large particles :. We find that
: is the primary determinant of crystal type due to energetic
interactions and interstitial site filling, while the number of grafted chains
per small particle determines the stability of these crystals. We observe
first-order sublattice delocalization transitions as T increases, in which the
host lattice transforms from low- to high-symmetry crystal structures,
including A20 to BCT to BCC, Ad to BCT to BCC, and BCC to BCC/FCC to FCC
transitions and lattices. Analogous sublattice transitions driven primarily by
lattice vibrations have been seen in some atomic materials exhibiting an
insulator-metal transition also referred to as metallization. We also find
minima in the lattice vibrations and diffusion coefficient of small particles
as a function of :, indicating enhanced stability of certain crystal
structures for : values that form compounds.Comment: AE and HL-R contributed equally to this wor
Delocalization Transition in Colloidal Crystals
Sublattice melting is the loss of order of one lattice component in binary or
ternary ionic crystals upon increase in temperature. A related transition has
been predicted in colloidal crystals. To understand the nature of this
transition, we study delocalization in self-assembled, size asymmetric binary
colloidal crystals using a generalized molecular dynamics model. Focusing on
BCC lattices, we observe a smooth change from localized-to-delocalized
interstitial particles for a variety of interaction strengths. Thermodynamic
arguments, mainly the absence of a discontinuity in the heat capacity, suggest
that the passage from localization-to-delocalization is continuous and not a
phase transition. This change is enhanced by lattice vibrations, and the
temperature of the onset of delocalization can be tuned by the strength of the
interaction between the colloid species. Therefore, the localized and
delocalized regimes of the sublattice are dominated by enthalpic and entropic
driving forces, respectively. This work sets the stage for future studies of
sublattice melting in colloidal systems with different stoichiometries and
lattice types, and it provides insights into superionic materials, which have
potential for application in energy storage technologies.Comment: Hector Lopez-Rios and Ali Ehlen contributed equall
Modulation of ionic conduction using polarizable surfaces
Hybrid ionic-electronic conductors have the potential to generate memory
effects and neuronal behavior. The functionality of these mixed materials
depends on ion motion through thin polarizable channels. Here, we explore
different polarization models to show that the current and conductivity of
electrolytes is higher when confined by conductors than by dielectrics. We show
that the polarization charge location impacts electrolyte structure and
transport properties. This work suggests a mechanism to induce memristor
hysteresis loops using conductor-dielectric switchable materials.Comment: 5 pages, 4 figures, A. P. dos Santos and F. Jim\'enez-\'Angeles
contributed equally to this work and both are equal first author
Hedgehog Signaling in Tumor Cells Facilitates Osteoblast-Enhanced Osteolytic Metastases
The remodeling process in bone yields numerous cytokines and chemokines that mediate crosstalk between osteoblasts and osteoclasts and also serve to attract and support metastatic tumor cells. The metastatic tumor cells disturb the equilibrium in bone that manifests as skeletal complications. The Hedgehog (Hh) pathway plays an important role in skeletogenesis. We hypothesized that the Hh pathway mediates an interaction between tumor cells and osteoblasts and influences osteoblast differentiation in response to tumor cells. We have determined that breast tumor cells have an activated Hh pathway characterized by upregulation of the ligand, IHH and transcription factor GLI1. Breast cancer cells interact with osteoblasts and cause an enhanced differentiation of pre-osteoblasts to osteoblasts that express increased levels of the osteoclastogenesis factors, RANKL and PTHrP. There is sustained expression of osteoclast-promoting factors, RANKL and PTHrP, even after the osteoblast differentiation ceases and apoptosis sets in. Moreover, tumor cells that are deficient in Hh signaling are compromised in their ability to induce osteoblast differentiation and consequently are inefficient in causing osteolysis. The stimulation of osteoblast differentiation sets the stage for osteoclast differentiation and overall promotes osteolysis. Thus, in the process of developing newer therapeutic strategies against breast cancer metastasis to bone it would worthwhile to keep in mind the role of the Hh pathway in osteoblast differentiation in an otherwise predominant osteolytic phenomenon
Erosive cola-based drinks affect the bonding to enamel surface: an in vitro study
Objective: This study aimed to assess the impact of in vitro erosion provoked by different cola-based drinks (Coke types), associated or not with toothbrushing, to bonding to enamel. Material and methods: Forty-six bovine enamel specimens were prepared and randomly assigned into seven groups (N=8): C- Control (neither eroded nor abraded), ERO-RC: 3x/1-minute immersion in Regular Coke (RC), ERO-LC: 3x/1-minute immersion in Light Coke (LC), ERO-ZC: 3x/1-minute immersion in Zero Coke (ZC) and three other eroded groups, subsequently abraded for 1-minute toothbrushing (EROAB-RC, EROAB-LC and EROAB-ZC, respectively). After challenges, they were stored overnight in artificial saliva for a total of 24 hours and restored with Adper Single Bond 2/Filtek Z350. Buildup coronal surfaces were cut in 1 mm2 -specimens and subjected to a microtensile test. Data were statistically analyzed by two-way ANOVA/Bonferroni tests (α=0.05). Failure modes were assessed by optical microscopy (X40). The Interface of the restorations were observed using Confocal Laser Scanning Microscopy (CLSM). Results: All tested cola-based drinks significantly reduced the bond strength, which was also observed in the analyses of interfaces. Toothbrushing did not have any impact on the bond strength. CLSM showed that except for Zero Coke, all eroded specimens resulted in irregular hybrid layer formation. Conclusions: All cola-based drinks reduced the bond strength. Different patterns of hybrid layers were obtained revealing their impact, except for ZC
The prevalence and risk indicators of tooth wear in 12- and 15-year-old adolescents in Central China
Massive and massless charge carriers in an epitaxially strained alkali metal quantum well on graphene
We show that Cs intercalated bilayer graphene acts as a substrate for the growth of a strained Cs film hosting quantum well states with high electronic quality. The Cs film grows in an fcc phase with a substantially reduced lattice constant of 4.9 angstrom corresponding to a compressive strain of 11% compared to bulk Cs. We investigate its electronic structure using angle-resolved photoemission spectroscopy and show the coexistence of massless Dirac and massive Schrodinger charge carriers in two dimensions. Analysis of the electronic self-energy of the massive charge carriers reveals the crystallographic direction in which a two-dimensional Fermi gas is realized. Our work introduces the growth of strained metal quantum wells on intercalated Dirac matter