470 research outputs found
Influence of an adsorbing polymer in the aging dynamics of Laponite clay suspensions
Clay-polymer dispersions in aqueous solutions have attracted a great interest
in recent years due to their industrial applications and intriguing physical
properties. Aqueous solutions of bare Laponite particles are known to age
spontaneously from an ergodic state to a non ergodic state in a time varying
from hours to months depending on Laponite concentration. When a polymer
species like Polyethylene Oxide (PEO) is added to the solution, it weakly
adsorbs on clay particle surfaces modifying the effective interaction potential
between Laponite particles. A dynamic light scattering study, varying polymer
concentration at fixed polymer molecular weight (Mw=200.000 g/mol), has been
performed in order to understand the effect of polymer on the aging dynamics of
the system. The results obtained show that arresting phenomena between clay
particles are hindered if PEO is added and consequently the aging dynamics
slows down with increasing PEO concentration. This process is possibly due to
the progressive coverage of the clay surface by polymers that grow with
increasing PEO concentration and may lead to steric stabilization.Comment: 13 pages, 6 figures, manuscript accepted for publication on
Philosophical Magazin
Routes to gelation in a clay suspension
The gelation of water suspension of a synthetic clay (Laponite) has been
studied by dynamic light scattering in a wide range of clay weight
concentration (Cw = 0.003-0.031). At variance with previous determination,
indicating a stable liquid phase for Cw < Cw*=0.015-0.018, we find that the
gelation takes actually place in the whole examined Cw range. More importantly,
we find that Cw* marks the transition between two different routes to gelation.
We hypothesize that at low concentration Laponite suspension behaves as an
attractive colloid and that the slowing down of the dynamics is attained by the
formation of larger and larger clusters while at high concentration the basic
units of the gel could be the Debye Huckel spheres associated to single
Laponite plates.Comment: 5 pages, 4 figure
More on phase diagram of Laponite
The phase diagram of a charged colloidal system (Laponite) has been
investigated by dynamic light scattering in a previously unexplored range of
salt and clay concentrations. Specifically the clay weight and salt molar
concentrations have been varied in the ranges Cw=0.004- 0.025, Cs=(1x 10^-3- 5x
10^-3) M respectively. As in the case of free salt water samples (Cs= 1x 10^-4
M) an aging dynamics towards two different arrested phases is found in the
whole examined Cw and Cs range. Moreover a transition between these two
different regimes is found for each investigated salt concentration. It is
clear from these measurements that a revision of the phase diagram is necessary
and a new "transition" line between two different arrested states is drawn.Comment: 16 pages, 5 figures, submitted to Langmui
Competing interactions in arrested states of colloidal clays
Using experiments, theory and simulations, we show that the arrested state
observed in a colloidal clay at intermediate concentrations is stabilized by
the screened Coulomb repulsion (Wigner glass). Dilution experiments allow us to
distinguish this high-concentration disconnected state, which melts upon
addition of water, from a low-concentration gel state, which does not melt.
Theoretical modelling and simulations reproduce the measured Small Angle X-Ray
Scattering static structure factors and confirm the long-range electrostatic
nature of the arrested structure. These findings are attributed to the
different timescales controlling the competing attractive and repulsive
interactions.Comment: Accepted for publication in Physical Review Letter
Frail old patients as a target population for cancer trials
The recent distinction between co-morbidity and multi-morbidity well stresses the difficulty of managing old patients with cancer whose complexity is not captured by a list of diagnoses or biological burden alone. The most adequate answer found by oncologists and geriatricians was to work together for better evaluating the physiological age and body reserve of the patient. The gold standard tool to assess old patient with cancer is named Comprehensive Geriatric Assessment. Its systematic application needs geriatric competences and time. In this context, a great number of cancer patients are considered as "frail” because they have reduced available physiological reserves. They might not withstand stress when challenged. Oncologists and geriatricians have imagined an innovative process to change the screening procedure of these patients, determine the prognosis, adapt the treatment strategy, to increase the patient's survival and his/her quality of life. The internet website "www.clinicaltrials.com” only lists 8 studies focused on frail elders with cancer. Six of them are focused on specific cancers or specific treatments, one was applied to all kind of cancers and the last was an opinion overview from oncologists and geriatricians. The selection criteria of frail patients are very diverse and probably include cancer patients who are not comparable. It is now time to try to identify new practical, reliable and accurate tools to facilitate the inclusion of the same kind of patients suffering from the same kind of cancer to be able to give more appropriate care and at the same time to constitute a valuable data base. Existing tools are reviewed and analyze
Arrested state of clay-water suspensions: gel or glass?
The aging of a charged colloidal system has been studied by Small Angle
X-rays Scattering, in the exchanged momentum range Q=0.03 - 5 nm-1, and by
Dynamic Light Scattering, at different clay concentrations (Cw =0.6 % - 2.8 %).
The static structure factor, S(Q), has been determined as a function of both
aging time and concentration. This is the first direct experimental evidence of
the existence and evolution with aging time of two different arrested states in
a single system simply obtained only by changing its volume fraction: an
inhomogeneous state is reached at low concentrations, while a homogenous one is
found at high concentrations.Comment: 5 pages, 2 figure
Juvenile diabetes and systemic sclerosis: just a coincidence?
Background: Limited joint mobility (LJM), previously known as cheiroarthropathy, refers to the presence of reduced extension at the finger joints in people with diabetes and may be associated with scleroderma-like syndromes such as diabetic sclerodactyly. While scleroderma-like syndromes and LJM have been observed in patients with long-term diabetes and associated complications, the coexistence of diabetes with Juvenile systemic sclerosis (jSSc) is rarely described. Case presentation: We describe the case of a 14-year-old boy with long-lasting type 1 diabetes (T1D) and suspected LJM associated with Raynaud phenomenon, sclerodactyly and tapering of the fingertips. A comprehensive work-up showed positive autoantibodies (ANA, anti-Ro-52, anti-Mi-2b), abnormal nailfold capillaroscopy with a scleroderma pattern, interstitial lung disease and cardiac involvement. The overall clinical picture was consistent with the diagnosis of jSSc. Conclusions: LJM can be the initial sign of underlying systemic sclerosis. Nailfold capillaroscopy may help differentiate jSSc from classical LJM in pediatric patients with T1D and finger contractures or skin induration of no clear origin. This case report provides a starting point for a novel hypothesis regarding the pathogenesis of jSSc. The association between T1D and jSSc may be more than a coincidence and could suggest a relationship between glucose metabolism, fibrosis and microangiopathy
Complementary and alternative medicine (CAM) in pediatric rheumatology: an European perspective
To analyse the use of complementary and alternative medicine (CAM) in children with rheumatic diseases, treated at a paediatric rheumatology centre in Italy
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