Through the looking glass: Unravelling how ions move in phosphate glass


Date:
August 10, 2021
Source:
Nagoya Institute of Technology
Summary:
Phosphate glasses are expected to have applications in a variety
of fields. To improve their functionality, it is necessary to
determine the association between their structure and ion diffusion
characteristics.

Recently, using first-principles molecular dynamic simulations,
researchers have provided novel insights into the ion diffusion
mechanisms of phosphate glass, suggesting that ionic conductivity
and glass solubility can be manipulated by controlling the
morphology of the material.



FULL STORY ========================================================================== Phosphate glass is a versatile compound that has generated interest
for its use in fuel cells and as biomaterials for supplying therapeutic
ions. P2O5-the compound that forms the structural network of phosphate
glass, is made up of phosphorus, an element that can adopt many different bonding configurations in combination with oxygen.


==========================================================================
The physicochemical properties crucial for the real-life applicability
of phosphate glass -- for instance, the hydration reaction dictating
how quickly a phosphate glass-based biomaterial will dissolve inside
the body -- depends on the diffusion of ions into the glass. Thus,
to improve the physicochemical properties of phosphate glasses, it
is important to understand the relationship between the structure and
ion diffusion. However, studying such interactions at the atomic level
is extremely difficult, prompting scientists to search for a suitable
approach to illuminate the details of the ion diffusion process.

Recently, a team of researchers from Nagoya Institute of Technology,
led by Dr.

Tomoyuki Tamura, has theoretically deciphered the ion diffusion mechanism involved in the hydration reaction process of phosphate glasses. Their
study has been published in the Physical Chemistry Chemical Physics
journal.

In fully connected P2O5-based phosphate glass, three of the oxygen atoms
in each phosphate unit are bonded to neighboring phosphorus atoms. To
study the dynamics of ions in the phosphate glass during the hydration
process, the researchers used a model made of phosphates with QP2 and
QP3 morphologies, that contain two and three bridging oxygens per PO4 tetrahedron, respectively, along with six coordinated silicon structures.

The researchers implemented a theoretical computational approach known
as "first-principles molecular dynamic (MD) simulation" to investigate
the diffusion of proton and sodium ions into the glass. Explaining
the rationale for their unconventional approach, Dr. Tamura says, "First-principles MD simulation enabled us to assume the initial
stage of water infiltrating and diffusing into silicophosphate glass
and elucidate the diffusion of protons and inorganic ions for the
first time." Based on their observation, the researchers proposed a
mechanism where the protons "hop" and are adsorbed onto the non-bridging
oxygen or "dangling" oxygen atom of nearby phosphates through hydrogen
bonds. However, in the phosphate glass model they used, the QP2 phosphate
units contributed more strongly to the diffusion of protons than the QP3 phosphate units. Thus, they found that the morphology of the phosphate
network structure, or the "skeleton" of the glass, greatly affects the diffusion of ions. They also noticed that when a sodium ion was present
in the vicinity, the adsorption of a proton onto a QP2 phosphate unit
weakened the electrostatic interaction between sodium andoxygen ions,
inducing the chain diffusion of sodium ions.

The demand for new biomaterials for effective prevention and
treatment is on the rise, and phosphate glasses are well-poised to
fulfill this growing need. A large proportion of the population,
comprising both elderly and younger people, suffers from diseases
related to bone and muscle weaknesses. As Dr. Tamura surmises,
"Water-soluble silicophosphate glass is a promising candidate for
supplying drugs or inorganic ions that promote tissue regeneration,
and our study takes the research in glass technology one step
nearer towards realizing the goal." Thus, the researchers' novel
insights are bound to have profound real-life impact and lead to
breakthroughs in research on fuel cells and bioresorbable materials! ========================================================================== Story Source: Materials provided by Nagoya_Institute_of_Technology. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Kazuya Takada, Tomoyuki Tamura, Hirotaka Maeda, Toshihiro Kasuga.

Diffusion of protons and sodium ions in silicophosphate
glasses: insight based on first-principles molecular dynamic
simulations. Physical Chemistry Chemical Physics, 2021; 23 (27):
14580 DOI: 10.1039/d1cp01646f ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210810121102.htm

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