Mol­lusc shells in­spire su­per-glass

The Star Malaysia - Star2 - - SCIENCE - By MARIETTE LE ROUX

ENGI­NEERS in­trigued by the tough­ness of mol­lusc shells, which are com­posed of brit­tle min­er­als, have found in­spi­ra­tion in their struc­ture to make glass 200 times stronger than a stan­dard pane.

Counter-in­tu­itively, the glass is strength­ened by in­tro­duc­ing a net­work of mi­cro­scopic cracks, ac­cord­ing to a study pub­lished in the jour­nal Na­ture Com­mu­ni­ca­tions last week.

A team at McGill Univer­sity in Mon­treal be­gan their re­search with a close-up study of nat­u­ral ma­te­ri­als like mol­lusc shells, bone and nails which are as­ton­ish­ingly re­silient de­spite be­ing made of brit­tle min­er­als.

The se­cret lies in the fact that the min­er­als are bound to­gether into a larger, tougher unit.

The bind­ing means the shell con­tains abun­dant tiny fault lines called in­ter­faces.

Out­wardly, this might seem a weak­ness, but in prac­tice, it is a mas­ter­ful de­flec­tor of ex­ter­nal pres­sure.

To take one ex­am­ple, the shiny, in­ner shell layer of some mol­luscs, known as nacre or mother of pearl, is some 3,000 times tougher than the min­er­als it is made of.

“Mak­ing a ma­te­rial tougher by in­tro­duc­ing weak in­ter­faces may seem coun­ter­in­tu­itive, but it ap­pears to be a uni­ver­sal and pow­er­ful strat­egy in nat­u­ral ma­te­ri­als,” the pa­per said.

Tak­ing what they learnt, the team used a 3D laser to en­grave mi­cro­scopic fis­sures into glass slides, filled them with a poly­mer, and found it made them 200 times tougher.

The glass could ab­sorb im­pacts bet­ter – yield­ing and bend­ing slightly in­stead of shat­ter­ing.

“A con­tainer made of stan­dard glass will break and shat­ter if it is dropped on the floor.

“In con­trast, a con­tainer made of our bio-in­spired glass has the pos­si­bil­ity to de­form a lit­tle, with­out com­pletely frac­tur­ing,” study co-au­thor Fran­cois Barthe­lat told AFP.

“That con­tainer could there­fore be used again af­ter one or sev­eral drops.”

The en­graved glass can “stretch” by al­most 5% be­fore snap­ping – com­pared to a strain ca­pac­ity of only 0.1% for stan­dard glass.

The stronger glass may find ap­pli­ca­tion in bul­let-proof win­dows, glasses, or even smart­phone screens.

Glass is func­tional be­cause of its trans­parency, hard­ness, re­sis­tance to chem­i­cals and dura­bil­ity but the main draw­back is its brit­tle­ness.

The new method to ad­dress this weak­ness was “very eco­nom­i­cal,” said Barthe­lat.

“All that is needed is a pulsed laser beam which can be ac­cu­rately fo­cused at pre­de­ter­mined points. Our 3D laser en­grav­ing tech­nique can eas­ily be scaled up and ap­plied to larger and thicker com­po­nents of dif­fer­ent shapes.”

Pre­vi­ous at­tempts to copy the sturdy struc­ture of mol­lusc shells had fo­cused on cre­at­ing new ma­te­ri­als by as­sem­bling minis­cule “build­ing blocks” – like build­ing a mi­cro­scopic wall. — AFP

The in­tri­cate mi­crostruc­ture of nacre, or mother of pearl, makes the sub­stance 3,000 times tougher than the min­er­als it is made of. — Wiki­me­dia Com­mons/Fabian Heine­mann

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